One of the scenes shows "The Big Guy" looking at a computer monitor showing "STS-71" docked. STS-71 was a mission involving Atlantis docking with the Mir space station in 1995, several years prior to the movie's time frame.
When discussing her beliefs with the guys, Ruth says that the world is 4,000 years old and can only be the product of intelligent design. Most Creationists believe that the world was created in 4004 BC, meaning that it is a little over 6,000 years old, not 4,000.
When Paul is going through the fridge for the first time in the RV, you hear Paul say, "Cool, Marmite." But the jar he pulls out of the fridge is actually a jar of Vegemite, the Australian version of Marmite.
When Paul is trying to push Agent Haggard off the road with the RV, Haggard has a small cut on his forehead. His car runs over some rough grass then back onto the highway, and the cut is suddenly twice the size.
After Tara's house explodes and Greame is running alongside the RV, the rear window is closed. Then when he is reaching towards Clive and says "Don't leave me!", the window is open. A second later when Clive pulls him inside, the window is closed again.
At the end of the movie when the chopper is landing, there are two pilots, two door gunners and, of course, the big guy is inside. Only one pilot, two gunners and the big guy ever come out. The co-pilot is never seen.
When Clive and Graeme pull over after Paul wrecks the black car, headlights can be seen just coming over the rise behind them. In the next shot as they clamber out of the RV, the road behind is suddenly deserted.
When Agent Zoil does a high-speed u-turn (handbrake turn) on the highway, the camera cuts to a close-up of him driving. You can see that he is driving on the right side of the car, instead of the left side.
When the special agent gets shot towards the end of the movie, there is a large bullet hole, with visible blood, and a torn jacket where the bullet went in. Later when Paul is getting onto the space craft waving goodbye, the bullet hole, blood, and suit are now all gone and cleaned up. As if it was never there. Taking into effect of what we know, Paul can heal, but I don't think he can mend clothing as well.
After Graeme and Clive leave the diner, Graeme gets in the RV after he said he was putting the alien on board sticker on the back. But after they crash into the pickup truck and drive past the ET highway sign, the sticker can't be seen on the back of the RV. Neither can the black mark that is left behind when Graeme later removes the sticker after they meet Paul.
When Paul and Ruth are arguing about religion after she comes to, there is a fly swatter and a green floral kitchen pocket hanging on the hooks on the wall behind Ruth. In the next shot, she grabs the fly swatter and the green floral pocket gets knocked down, but later in the same scene when we see Clive driving and he says "Oh yeah" it can be seen hanging there again.
After Clive buys the "Black Vampire" sword in the comics shop and they are discovered by Agents O'Reilly and Haggard, Haggard is about to shoot Paul but is stopped when Clive body checks him. In this scene, Clive is shown holding nothing in his hands. However, in the subsequent shot of Clive and Paul running out of the store, Clive is now clutching the sword.
The rude drawing th at Mr. Buggs picks up when it flies out of the RV has creases and damage to the holes at the top right but when it's seen from beside him four seconds later, the creases and damage is on the left. Later, when Haggard finds it in Buggs' back room the creases and damage are gone, and later on in the movie when Haggard shows it to Gus and Jake, the damage is only on the right side but less than when Mr. Buggs first picks it up.
After the Big Guy and crew get out of the helicopter we can see that the blades are idling in the background. A couple of seconds later the blades are stationary. It takes a lot longer than that time for helicopter blades to come to a complete stop.
After the Big Guy and crew get out of the helicopter we can see that the blades are idling in the background. A couple of seconds later the blades are totally stopped. It takes a lot longer than that time for helicopter blades to come to a complete stop.
In a night scene when the camera is looking through the front of the RV, a soft box rigged to the front right of the vehicle (as side/back light to the passenger seat) can be seen dipping in and out of frame, then finally completely into view.
When Zoil receives information on where to locate Paul he locks up the brakes on his black Ford Crown Vic and slides the car into a smoky 180 degree turn. Under the right side rocker panel 3 stunt dolly wheels are visible.
While riding for the first time in the RV, Paul states that the car accident was due to his not being able to reach the pedals, and that he therefore "needed to use the parking brake." The parking brake on the Crown Vic is a pedal located to the far left. There is no lever-operated parking brake.
When Haggard and O'Reilly are at the road block there are several Saguaro cactuses in the shot. They are suppose to be in Nevada, but the Saguaro cactus only grows in the Sonora desert, which would be central/southern Arizona into Mexico.
When Graeme and Clive are having lunch at Comic Con, we see Baskin-Robbins and Hot Dog On A Stick food vendors. Other than Starbucks and Mrs. Fields Cookies, the San Diego Convention Center does not let outside food vendors inside the building. They have their own café selling sandwiches, pizza and salad.
The state trooper's car says "Nevada State Police" on the side, and his uniform shoulder patch reads "State Police." Nevada has no state police. There is a state department of public safety, which has a highway patrol as one of its divisions.
One of the climactic scenes was when Paul tells his new friends why he is running & where he is going, but at that point in the movie he had already transferred his cumulative knowledge on to all of them so they should have known already. Although Paul is capable of transferring his knowledge to other people it could easily be possible that Paul may limit the knowledge he gives to others as to not give away all of his secrets such as why he is on Earth even to his friends as to protect them.
When trying to assault "The Big Guy" Clive breaks his sword. Later when they say farewell to Paul you can see the sword unbroken again on his back but Paul brings Graeme back to life and the aliens are shown healing the soldiers wounded by Zoil. With their powers and technology, fixing a broken sword for a friend would have certainly been child's play.
The huge explosion that rips through Tara's house isn't very likely. She only left the stove on for a short while, and if there was really a massive concentration of gas as depicted by the explosion, the Agent who fired the shot that triggered it should have collapsed from inhaling so much gas.
When Agent Zoil fires his weapon until emptied, and the slide locks open, he fires one more time and you can hear the weapon click, but this would not happen with the slide locked back in the open position.
When Graeme is convincing Ruth to go with them and she says "Where would I sleep?", you can see her left pupil through the dark lens: it moves as she looks to her right twice and then back. In the next scene, it is shown that she doesn't have a visible pupil in her left eye.