Continuity mistake: When David walks into his office, with Marty, he sits down at his desk, and the water bottle is in front of the computer monitor, to the left of the keyboard. In the next shot, when he picks up the bottle it has moved to the right side of the keyboard.
Continuity mistake: When President Whitmore boards the chopper and then Air Force One, he wears a white shirt with both thin and thick stripes. The stripes on his shirt collar constantly change, and nowhere is it more noticeable than when they arrive at Area 51. It varies between only one thick stripe, which changes from the top of the collar to the bottom, or two or more thick stripes, all surrounded by thin stripes. Wardrobe Dept bought identical shirts for the actor to wear, but the collar stripes just don't match up between scenes.
Continuity mistake: Julius and David are driving in the Plymouth and when they reach DC, the car's rearview mirror is visible from the back, but in the next close-up as they pull up in front of the White House gate, the rearview mirror has vanished.
Continuity mistake: When David squeezes his dad's shoulder, after he just won chess, David has a severe bruise on the middle fingernail of his left hand, which disappears as soon as he gets back to work.
Continuity mistake: In the Oval Office, when David says, "They're using our own satellites against us," the grandfather clock is about a foot away from the doorway behind him. In the previous wideshot, when Alex appears at the doorway, the grandfather clock is farther to the right, nearer to the other curtained doorway.
Continuity mistake: When David and Steven are on their way to the mothership, in shots facing David's right side the black safety harness and metal clasp are upside down, but in other shots the harness and clasp are on properly.
Continuity mistake: While David is talking to his wife, he holds the Johnny Walker bottle in his hand, then it is suddenly on the window sill.
Continuity mistake: Air Force One's cabin window shades move up/down when President Whitmore and Connie are talking, beside the President's sleeping daughter, and when the President asks General Grey for an update about his wife's whereabouts.
Continuity mistake: After their daughter leaves the room, when the President tries to lie to the First Lady about her condition, her hand is touching his face in the shot facing her. In the next shot facing him, her hand is down holding his hand, but when it cuts away her hand is back up touching her husband's face.
Continuity mistake: At the start, when the SETI Chief arrives at the lab (after being awakened), a SETI tech sits on the desk in front of the window blinds, which are pulled up (shoulder height). Next shot facing him, those blinds are pulled all the way down.
Continuity mistake: When Russell boards the F/A-18 and when he is airborne - such as when he salutes Major Mitchell (who is back at command center), he wears his Hawaiian style short-sleeve shirt and is gloveless. After he says, "Eagle 20, Fox 2," in the close-up as he presses the launch button (resulting in launch failure), the arm shown wears both a green jumpsuit and gloves, neither of which Russell actually wears.
Continuity mistake: At the end of the movie, all the falling debris and the accompanying firetrails change color all at once.
Continuity mistake: When David shows up at his father's house, Julius opens the door pointing a gun at his son. David grabs hold of the barrel and in the shots facing Julius, David lets go, but in the shots facing David the barrel is still pointing up which David is still holding firmly.
Continuity mistake: At the decimated MCAS El Toro, when the First Lady asks Jasmine what she does for a living, the First Lady holds the bowl out with her left hand in the shot facing Jasmine, but in her right hand in the shots facing facing her. The direction of the bowl's handle also changes.
Continuity mistake: As we hear the biplane's engine closing in on Miguel Casse, as he rides the motorbike down the road, in the overhead descending shot his shadow is to his right, but next shot as his crop-dusting father passes over him the shadow is to his left.
Continuity mistake: In the interior shot, when Jasmine tries to explain why she doesn't want Steven to leave she pulls open the white curtains, to view the alien ship through the window (the window closest to the door), and as Steven walks out the front door she stands by that open window. Then when it cuts to the exterior shot, in an instant that window's brown venetian blinds are now down and the white curtains are drawn closed, as Steven walks down the lawn.
Continuity mistake: The missile used in the mother ship had a 30 second count down. From time of launch to explosion was one minute thirty-six seconds.
Continuity mistake: After Major Mitchell is asked get a gun to shoot the Coke can, in shots facing David, the Major's body faces toward the alien attacker, but in shots facing the alien attacker Major Mitchell's body is turned the opposite way.
Continuity mistake: After going to the bathroom, when Steven turns on the TV in the kitchen, in the TV's close-up before the program comes on, the kitchen's reflection is visible. In the reflection something is lying on the stove (beside the fridge) and a chair is in front of the corner door, but when it cuts to Steven opening the fridge door, they're gone.
Continuity mistake: When the spaceships begin arriving, it is obviously morning in Los Angeles. Will Smith and his girlfriend are still in bed, and later on Will goes out to get the morning paper, etc. Jeff Goldblum has just said that the countdown will be over in roughly 7 hours, so how is it night in LA when the spaceship finally attacks?
Answer: Remember that the aliens had to interface with our satellite computer code first...David simply "reverse engineered" the code to create the virus. When it was uploaded, they didn't have enough time to combat it.