Continuity mistake: Throughout the film, especially inside the spaceship when its flying, the boy's hair goes from short to long in fact he is at least 6 months to a year older facially too.
Continuity mistake: As David and the ship are leaving the NASA hanger, the straps that are holding the ship down start to break. From the shot outside the ship, you can plainly see the straps hanging on the front off the ship, but from inside the ship looking out the front "viewscreen" you see a clear picture, with no straps obstructing the view.
Continuity mistake: After David has relieved himself, he and Max start a heated conversation about why the computer hadn't returned David back to his own time; a herd of cows grazes nearby. Towards the end of the debate, a cow can be seen near the ship's hatch in a close-up; in a wide shot, the cow is gone; and in a second close-up, the cow stands near the hatch again.
Factual error: When the alien craft speeds away from the NASA base, its slipstream tears off the roof of a small booth. But the wake also should sweep the people in its flight path down to the ground; it is too close for that not to happen.
Continuity mistake: When Dr. Faraday and the radar technicians are monitoring David's ship as it free falls towards the U.S. west coast, take a look at their glasses and you'll notice how a map of Japan is being reflected instead (needless to say, the exact same image is reflected three minutes later when the ship enters Tokyo airspace). (01:04:30)
Revealing mistake: Many times during the movie, when there is a close-up of the puckmarin, tiny wires can usually be seen attached to its arms.
Continuity mistake: When David is in the ship at the NASA hanger, just as Dr. Farraday asks him to get out of the ship, the door closes. From outside the ship, the interior is pitch black, but in the very next shot from inside the ship, it is lit up from the front "viewscreen" and various lights on the wall, which should have been visible as the door closed.
Visible crew/equipment: When David starts to navigate the ship, watch the metal wall behind him, and you will be able to see the camera crew and realize that the spaceship is a prop by seeing a black wall behind the camera.
Continuity mistake: The three-digit code on the police car which takes David to his parents' new home changes. Just before it parks by the house, it makes a left turn near the highway. Here we can see its number is 442. But when Detective Banks exits the car, the number is partially visible - with the last two digits being 51 instead of 42. (00:14:30)
Continuity mistake: When Dr. Faraday is talking to David and his family along the New River in Ft. Lauderdale about going to the NASA facility, in the beginning of conversation up until when David says "no" the Andrews Ave. draw bridge in the background is down. When Dr. Faraday convinces David to go to find out where he's been 30 seconds later, the bridge is open/up and is closing/going down during the rest of the conversation. (00:27:30)
Factual error: After David's ship breaks free and exits the hangar, he orders Max to take him 20 miles away. Back at the tracking room a technician informs Dr. Faraday that the ship has gone 20 miles straight up, but the target altitude indicated on the screen reads 184,800 feet - more than a 35 mile distance. (00:52:00)
Continuity mistake: Right before David sets out to meet up with Jeff in the woods, he's out on the front lawn feeding Bruiser. It eats everything on the tray, save for a couple of pieces - but when Helen calls for David from the patio in the following shot, the tray is nearly filled with dog food all of a sudden. (00:07:10)