1. When Will Smith throws a rock at the escaping Edgar alien, if you watch the rock after it hits the alien, it disappears after hitting the ground.
2. When Will Smith is looking at the two space ships at the MIB headquarters, if you look in the background Zed and K are there typing on the computer. But if you look closer you can tell that they’re not even touching the keyboard and the sounds are just added into the movie.
3. Just before the diner scene, where the two aliens are discussing the galaxy, we see the outside of the Russian restaurant. The neon sign says “haroshaya” meaning “good” all the way across the window, in the next shot inside the restaurant, the “ha”, which looks like the English letters “xo”, is gone and the sign is centered.
4. When the Bug’s spaceship floats over Shea Stadium and the NY Mets outfielder sees it and gets conked on the head by the fly ball, he is wearing number 23. In a later scene, when J picks up the tabloid newspapers, the photo of the ballplayer has number 20.
5. When the jeweller leaves his shop, the shop window clearly shows the reflection of the parked exterminator’s van. Then you see the van being driven up the cross-street as the jeweller leaves in the taxi. Then Edgar/bug parks the van, goes to the shop, and you can see the same reflection in the jewellery shop window.
6. When Tommy Lee Jones shakes the dog asking him about the galaxy, right before they exit the car, you can see the cameraman’s reflection in the shiny black door frame.
7. When Will Smith and the other recruits are taking their written tests, the white table first appears to be situated between the second and third men from the left. When Smith goes to the table to pull it across the room, it is much further to the right of the scene.
8. When Will Smith is holding the squid, watch the reflection on the alien’s black eyes. Although Will Smith is standing alone, the reflection on the eyes shows two people, or – depending on the shot – one with a big hat.
9. When the truck gets smashed at the start, the tree beside the truck is well alight, but when the man comes out of the house, it is only a little alight.
10. When the countdown timer for the destruction of Earth appears on the viewscreen, you see it count down to 59:56. There is a cut to three cast members including Will Smith and Tommy Lee Jones for a brief dialogue scene. When it cuts to Will Smith walking away you can see the clock still counting down on the screen in the background. Now it is showing the time of 59:54. The aforementioned dialogue section took noticeably longer than two seconds.