When "Keys" goes inside the Clean room created for ET and Elliot, he and others wear a "Clean Suit" , but the tubes coming out of the helmet go nowhere, not even a filter, meaning they are breathing contaminated air and that the suit is useless.
Near the beginning of the film, when the trucks race through the woods approaching the expected location of the spaceship landing, one of the trucks "screeches" when it stops. A vehicle's tires would not screech on wet, muddy ground.
After ET has apparently died, one of the medical staff is dictating a report and says; "Cardiac arrest was terminated at 1500 hours and 36 minutes". "Cardiac arrest" is a way of saying that the heart has stopped, so it makes no sense to stay that cardiac arrest had been terminated. The line should have been either; "Cardiac arrest occurred at 1500 hours and 36 minutes" or "Cardiac activity terminated at 1500 hours and 36 minutes".
In the 20th Aniversary Edition, when Eliott is showing E.T. the bathroom and is then on the phone with his mother, the Coke can changes designs. At first, it is the older version from 1982, then it changes to the updated 2002 can design. It switches back and forth for the entire length of the scene.
After one of the kids whips off his balaclava and says, "We made it!" during the bike chase, a hoard of government agents rush into the street behind him. In the next shot of Michael reacting, his friend takes off the balaclava again and the agents run into the street again.
Elliott is given money and told to wait for the pizza guy outside, indicating the pizza has been ordered and on its way. But a line or two later, the boys ask him to make sure he orders lots of pepperoni and sausage. He is then seen outside meeting the driver at the foot of the driveway.
When E.T. is alone in the house and misspells "nuisance" on the toy, we see that the back panel has been removed, but in the next shot the panel is back on. Later, when E.T. drags the blanket with the "phone" ingredients on it, the panel is back off.
When Gertie is waiting with the bike at the rendezvous, the sun is just about to set behind the mountains. Yet there is still plenty of daylight for the Halloween street scenes. The sun is then shown much higher above a smaller foothill. Finally, when the kids and E.T. meet up at the bicycle, the sun has just dropped below the mountain peak.
When Elliot disconnects the tunnel and two men from the back of the van, the men's air hoses remain attached to the van as it speeds away, however the air hoses are gone a second later when the van is shown from a different camera angle.
When Elliot thinks E.T. is dying, and is talking to him through the window of the box, the towel that is wrapped around Elliot keeps changing position - sometimes it is wrapped tightly around his neck, and other times it reveals a bit of his left side.
When Elliott and his brother first try to drive away in the government van and are caught, the agents crowd around and in front of the truck. But moments later the van drives off easily with no one in front of it.
When E.T. spies on Gertie and her mom reading the bedtime story, the set of blinds open in the closet door changes between shots. When we see E.T. from behind looking into the bedroom, the blinds in the middle of the door, just above his head are open. When we see E.T.'s face from the front, the blinds in the bottom third of the closet are open, at and below his eye level, and the middle blinds are closed. The set of open blinds changes back and forth between shots.
When E.T. is walking outside during Halloween, the eye holes on his sheet are far apart and only one is matched up to his eyes. However, the shots of what E.T. is seeing through his sheet show the two eye holes lined up close together.
Towards the end when the kids are riding bikes down the hill, after they ride past a cop car they round the corner behind a housing development and you can see "elliot" or the rider in the red hoodie wipe out. In the next scene they are riding as if uninterrupted.
When Elliot and E. T. have finished saying goodbye, Dee Wallace can be seen in the background rising to her feet (next to "keys"). The next shot is from a medium distance, and Wallace is once again shown rising to her feet.
In addition to the other lunar errors, at first we see a
crescent moon then the famous full moon being crossed by the bicycles (later to become Amblin Entertainment's signature logo). From thin crescent to full moon takes about half a lunar cycle, 14 days, but the time frame of the movie suggested only a few days at most.
Some are confused when E.T. magically heals Elliot's cut finger that the blood disappears. E.T.'s true powers are not fully known so it is possible E.T. made the blood go back into his body along with healing the wound.
[20th Anniversary edition] When E.T. is eating potato salad and drinking beer in front of the refrigerator during the scene when he is alone at home, the shadow of his head cast on the fridge door is that of the original puppet, not the CGI head.
When Elliot returns with a snack for a frightened E.T. hiding among stuffed animals in his toy closet and asks "want a Coke?", the stuffed animals around E.T. fall down, knocking off some chips from Elliot's plate on to the animals. There are already chips on one of the animals as it falls, before it has a chance to actually touch the plate (possibly left behind from earlier takes).
The goof items below may give away important plot points.
E.T.'s potted plant is suddenly much larger when Gertie and Mary are in the car right before the bicycle chase gets underway. The plant returns to its original, smaller size when Gertie gives it back to E.T. before he leaves.