Elliot: Okay, he's a man from outer space, and we're taking him to his spaceship.
Greg: Well, can't he just beam up?
Elliot: This is reality, Greg.
When the boys are riding their bikes trying to escape with ET, all the bikes have single brake levers on the right side of their handlebars, but after Elliott shouts that they should follow him to the forest, there's a shot from the POV of one of the bike riders (we know it's not Greg or Elliott) and he has two brake levers on his handlebar.
Steven Spielberg has a cameo as one of the doctors when Elliot and E.T. are 'hospitalized' inside the house.