When the Aliens come to take Barry we see a beam of red light shining through the keyhole. Presumably it moves to show the space ship landing. However if this were so the ray of light would start at the bottom and move upward, not as it is in the shot where it starts at the top and moves down.
In one scene, many people are on a hillside watching two bright lights approach them from near the horizon. As the lights get closer a few more lights with lower intensity can be seen trailing behind them. The next shot shows that at least the two brighter lights were military Huey helicopters which are shown hovering near and scattering the people. Huey helicopters have a very distinct and prominent "thump" generated by their rotors. The noise is very clear, especially if the chopper is headed directly towards the observer, and can be heard from a considerable distance from the aircraft. It's very doubtful that two Hueys, possibly followed by more, would be able to approach the observers as quietly as shown in the scene. The "Bell Thump" can be very reassuring if you're stuck in the weeds and need to get out of there fast. But, it doesn't make for a sneaky approach.
During the ABC newscast, a reporter states that the Devil's Tower National Monument was created by Theodore Roosevelt in 1915. Roosevelt was President from 1901 to 1909 and the Monument was created in 1906.
'Steven Spielberg (I)' and producers wanted Walter Cronkite as newsreader for the broadcast that Neary ignores in the "living room sculpture" scene. However, Cronkite's network would not allow him to take the role, so the producers settled on ABC's Howard K. Smith. Unfortunately, the news footage of the Wyoming reporter was filmed before this decision; as a result, the reporter says "Order your steak well-done, Walter."
When Roy starts gathering material for his "living room" model of Devil's Tower he throws a shrub through the kitchen window, which is shown shattering in an interior shot; yet, at the end of the scene, after he climbs through the kitchen window and pulls the ladder after he, he emphatically closes the same window, which is no longer broken.
In a close shot of the UN SUVs, one of the flags is blowing forward while the other blows backward. Also the flags are waving as if in a gentle breeze. In all the others shots the vehicles are moving fast and all the flags are blown back by the strong wind.
When the entities are attempting to get into Jillian's house, they pop the floor vent out of its hole and it lands upside down on the area rug. In the next shot the vent is back in its hole, even though Jillian hasn't touched it yet.
The size of the mother ship is incompatible in different shots. When it arrives it's behind the mountain and a lot bigger than the mountain. When it's in front of the mountain it's no longer bigger than the mountain but smaller or at best about the same.
When Roy is stalled at the railroad track, the mailboxes fly open and their contents are expelled (close shot of the mailboxes). When seen from the inside of Roy's truck, the mailboxes are closed. This repeats with successive shots from the inside of the truck (closed) and the outside view (open).
As the 12 people in red selected by the government head for the mothership, the blond woman is two people in front of Roy, and not wearing her sunglasses. In the next shot, she has her sunglasses on, and is now immediately in front of him.
Roy and Gillian climb a red clay embankment to get their first personal look at the Devil's Tower. The first view shows the Tower with a partly cloudy sky behind it. There is a cut to Roy and Jillian, then a cut back to the Devil's Tower. This time the sky behind the Tower is completely overcast.
After Roy drives through the fence, one of the posts lands on the hood. We see it fall off after he drives through another fence, but when he stops at the barricade it's back, along with a couple of other pieces of fence that weren't there before.
In the scene where Roy is first shown with his living room creation (model of Devil's Tower made with trash/bricks/chicken wire), looking through the porch door it is clearly raining (most noticeable by the rain dripping onto the can that's on the ground just outside the door). The TV is playing an episode of Days Of Our Lives. As DOOL goes to commercial (Budweiser commercial plays) Roy looks out the window. He looks out at people outside in their yards, and it is bright and sunny out.
In the first scene in the desert, although it appears to be around noon at the beginning, by the end of the scene the sun is clearly on the horizon and setting, even though only a short amount of script-time has passed.
At Devil's Tower, when the 3 smaller ships approach, the first flies in over Roy and Jillian, with the other two ships in the background. In the following reverse shot, the first ship is seen hovering over the landing area. The camera cuts back and the third ship already flies in. In the following reverse shot, all three ships are shown hovering over the landing area, but the second ship was never shown flying in.
Toward the end of the movie, when Jillian and Roy are at Devils Tower and the mother ship is descending, Jillian has her jacket tied around her waist. The jacket is present the whole time she is hiding in the rocks, watching what is going on the landing field. But in the next scene that she is in, when she is walking across the field to reach Barry, the jacket is gone.
During the first scene with the Nearys, Ronnie is sitting in a chair holding items she had removed from the breakfast table. The camera angle changes to Roy asking the boys to choose between goofy golf and Pinocchio. The angle changes back to Ronnie who is still sitting in the chair but is holding Sylvia.
When Roy's wife is taking the kids and backs down the driveway, she hits a Big Wheel and pushes it to the other side of the street, where it sits against the curb. We still see the toy when Roy is sitting on the ground, but as he stands and walks back towards his house, the Big Wheel has disappeared.
The mother ship is clearly several times larger than the circumference of Devil's Tower; therefore, it could not be hidden by it. The mother ship just appears out of nowhere, and the mass of clouds that appeared in the preceding shot are gone.
When Roy and Jillian climb the embankment to view Devils Tower, they both grab hold of the wooden posts of the fence that create an A-frame. In the very next shot, Roy is still holding onto a post but the post in front of Jillian is gone and she is holding onto the barbed wire instead.
The coordinates received by the scientists (40°36'10" N, 104°44'30" W) aren't very close to Devils Tower at all. The coordinates are very close to Stage Colorado, east of Ft. Collins, Colorado, almost 300 miles (480 km) away from the monument.
The scene where the Muncie police cars are chasing the UFOs shows them driving in mountains and through tunnels, and cross into the state of Ohio. Muncie has no mountains, no tunnels, and is not that close to Ohio. There is another county between Muncie and the Ohio state line. The Indiana Toll Road is about 100 miles north of Muncie, paralleling the Michigan state line.
One of the Air Traffic Controllers at the Indianapolis Center asks the Air Force if they have any tests going on in Restricted area 2508. R-2508 is in California and Nevada. It would be controlled out of Los Angeles Center.
Stars shown on a summer night near Muncie, Indiana are inappropriate for the latitude and the season as shown by the dense foliage. The constellation Orion would be much higher in the sky in the upright position in which it is shown - but only during the winter and late autumn.
When the numbers sent by the aliens are interpreted as geographic coordinates, there is no indication of the hemispheres of the latitudes nor longitudes. The coordinates as they are sent - 104°44'30" 44°36'10" - actually describe a point in north-central China.
While preparing for the evacuation, the military speaks of clearing 360 square miles, which would involve from 35,000 to 50,000 people. Later, a news report states that 200 square miles are being evacuated. Devils Tower is centrally located in Crook County, with an area of 2858 sq. miles and a population of 5887, and is over 15 miles from the nearest city. 200 sq. miles would be a circle of 8 miles radius. 360 sq. miles would be a radius of 11.5 miles. The actual population of the evacuated area would likely be less than a few hundred people, not 35 to 50 thousand.
In the opening scene when the aircraft from Flight 19 are found, the call is made to "get the numbers off the engine blocks." Engines were exchanged frequently so it is more likely they would look for the Aircraft numbers off the identification plates, which have been well published.
During the ABC newscast that Roy sees, the voice over on the videotape report says that "Devil's Tower was the first national monument erected in this country". Devil's Tower wasn't "erected" by anyone - it is a natural geologic formation of igneous rock which has been there for over one hundred million years. The announcer should have said "the first national monument designated in this country", not erected.
The plate on Roy's station wagon in Wyoming displays a 44 on the left of the bucking bronco logo. This is not a real plate. The numbers to the left of the logo on a Wyoming plate indicate the county in which it was issued. Wyoming only has 23 counties. The local county number for Devil's Tower (Crook County) would be 18. The most likely place he rented the car (Roy is from Indiana, The car has Wyoming plates) would be Gilette in Campbell County, which is 17.
Electrical utility workers are almost 100% represented by labor unions in the United States. This is especially true of Indiana, a bastion of organized labor in the 1970s. Neary would never have been summarily fired in the morning no matter what he did. Instead, he would have been put on leave (at worst unpaid but possibly paid) pending an investigation and a hearing with a union representative present.
The toll collector says that the toll is is 25 cents. The Indiana Toll Road is a ticket system (the toll is based on distance traveled). This would also preclude the sign indicating the price of the toll.
The aircraft used as Flight 19 in the opening scene are all TBM-3 Avengers. The real Flight 19 had only one TBM-3 and four TBM-1C aircraft. In fact, one of the aircraft in this scene is actually a F6F Hellcat.
In reality, when a child vanishes, the parents are the prime suspects after all other possibilities have been eliminated. After the authorities fail to locate Barry or his body, Gillian would be their prime suspect in his disappearance. She would never have been allowed to leave the state.
The solfege hand signals Lacombe and the alien use at the end of the film to "talk" to each other are in the wrong order. The first and second notes are switched and while it should be "re-mi-do-do-so", what is signaled is "mi-re-do-do-so".
At least two of the Navy fliers returned by the aliens at Devils Tower give their rank as "Captain, U.S. Navy Reserve." It's unlikely men that young at the time of their abduction would hold that rank; the filmmakers may have been intending to portray them as Marine Captains, the equivalent Navy rank being Lieutenant. Two of the missing pilots were indeed Captains in the Marine Corps.
The Special Forces soldiers and their commander do not have Special Forces emblems on their uniforms, they wear a mock up of the 5th Special Forces beret flash with the flag of South Vietnam, only worn in service in Vietnam.
When the mother ship slowly maneuvers into position over the landing base, overhead shots of the spectators show a large, ominous shadow drifting over the crowd. But being above the flood lights at night, and producing light of it's own, the opposite of a shadow effect would be cast by the ship.
When the UFOs go through the toll booth and the guard stands up, in the close up shot of his reaction the clock behind him on the wall is flipped, so the entire shot must be a "mirror image" for some reason or other.
In the climatic ending the first alien, a tall and spindly creature crawls out of the huge "mother" ship's opening, then stands up spreading its long arms out wide. It's a very memorable and dramatic cinematic entrance with the film's score adding to the grandeur. The smaller aliens come out and stand in line, then greet the humans. We do not see the first tall alien again in the film and in all released versions of Close Encounters of the Third Kind. However, Spielberg's intent was to show a racially diverse group of aliens aboard the ship, as evidenced by the final alien who communicates with Lacombe, who is also a physically different character than the tall and small aliens. The tall alien was not meant to resemble a spider, but was referred to by the production team as the "Jesus alien" because of its arms-out gesture. There were originally supposed to be three of them, joining hands in that position and creating more shimmering lights. The production team simply could not make this work. This alien was a marionette, and it was very difficult to film without the strings showing.
The newspaper headline describing Barry's abduction reads "Cosmic Kidnaping" rather than "Kidnapping". This is not a misspelling but a now-uncommon variant that some publications still used in the 1970s (Time Magazine used it well into the '90s).
While it's true the Helvetica typeface was not designed till the 1950s, the calendar at the beginning scene may not be wrong. It's set in a sans-serif typeface but it's not clear it's Helvetica, and there were other typefaces from the time that looked the way that calendar does.
When Jillian has caught up to Barry on the highway and almost gets hit by Roy, the three stars in a row which appear to be Orion's belt that are visible above a tree to the right of the screen repeatedly change position between shots. In the book, however, the alien visitors are, in fact, described as being from the Orion constellation, so those "stars" could very well be alien ships, as, in the book, they use the ships to show where they came from.
From Muncie, Indiana (Roy's town) to Moorcroft, Wyoming (outside Devil's tower) is 1,250 miles and would have taken at least two full days to drive; yet, Roy is showing arriving at Moorcraft the next day in the late morning. Later, though, we can see the car he is driving has Wyoming plates, indicating that he flew to Wyoming and rented a car when he arrived.
When Roy is in his truck, the maps and papers get blown off of his dashboard and then he speeds away. When he stops his truck upon meeting Jillian and her son, everything is stacked very neatly on top of the dashboard. It's possible, though, that he stopped between the two locations to clean up his truck.
Shortly before Barry Guiler is abducted from his house by aliens, we see electrical appliances moving and powering themselves. In the kitchen, the stove rings are meant to be glowing, however they cast a shadow on the rear panel of the stove - indicating that the rings are actually cold, and being lit from underneath with red lights.
After one of the police cars runs off the side of the road chasing the four smaller UFOs, Roy's truck and two police cars skid to a halt. All three vehicles skid at equally 45 degree angles. (\) In the next shot, which overlooks the greater Muncie area, you see the UFOs disappearing in the mountains while the city grids start to light up again. Roy's truck is now parked at a -45 degree angle. (/)
The American flag patch on the uniforms of the volunteers at the end of the film are backwards. The camera pans down the row of volunteers in their jumpsuits and each has a flag patch on their right shoulder with the stars on the left side of the flag. When a flag patch is worn on the right shoulder, the stars should be on the right side of the flag with the stripes pointing to the left.
On the highway at night, three police cars speed by, and Roy says, "This is nuts!" He walks to his company truck and opens the passenger side door, the scene cuts, and we hear it close, followed by the ignition. It appears he got in by the passenger side door.
The goof item below may give away important plot points.
Incorrectly regarded as goofs
When the Mothership opens and abducted people come out, the first ones are apparently the missing pilots from, Flight 19, the training flight in 1945 whose planes were found in the opening scene. The names of the crewmen do not match the actual names. The closest is "Frank Taylor", actual crewman was Charles Taylor. Also named in the movie was Robert F. Landham, actual crewman was Robert F. Gallivan. Others named in the movie that have no close actual counterparts were Harry Ward Craig, Matthew McMichael and David Erickson. This could easily be explained as, when the second returned person walks past, they show a board having multiple abductees, not just the 5 from Flight 19. In fact, it could be that there were many other planes and boats that crew members were returned from as the shots go to Neary getting set for his journey.