Audio problem: 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.
Continuity mistake: 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.
Continuity mistake: 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.
01:20:15 - 01:29:20
Continuity mistake: 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.
Visible crew/equipment: In the scene in the beginning where Will Smith chases the alien who jumps off the bridge onto the street. Will Smith jumps from the bridge onto a tour bus, then jumps on the back of a newspaper delivery van. In the passenger side of the van is a cameraman with his back towards the windshield in order to film down the side of the van as Will Smith jumps off the van.
Continuity mistake: 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.
Continuity mistake: 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.
Continuity mistake: When J is changing in to his suit, he reaches in to the locker with his right hand and pulls out a hanger with a pair of trousers and a jacket on it. His forearm is bare and he isn't wearing a watch. Seconds later when he takes the shoes out of the locker with his left hand, his forearm is now covered by the long sleeve of a white shirt and he has a silver watch on. A few seconds later when he lays the jacket over the bench, both his forearms are bare and again he isn't wearing a watch.
Revealing mistake: When J and K get into the car (a POS if memory serves) K makes a comment about J fastening his seatbelt, if you watch in the background out of J's window as they pull away there are a few people walking at an incredible rate showing that they filmed the scene at a normal speed then sped it up when put into the final cut.
Other mistake: In the final scene outside the MIB headquarters, Kay opens the neuralizer and we see it open, but there is no sound. Later when Kay tells Jay that he hasn't been training a partner but a replacement, we hear the sound of the neuralizer opening and Kay tells Jay how to operate it.
Continuity mistake: Throughout the whole movie it is summer. Green trees with leaves, green grass, etc. After the scene where Will Smith is deciding to become a Man in Black (summer), there is a shot of the Bug Mobile driven by Edgar where it is obviously winter. A wide shot of Manhattan with steam coming out of the tops of some of the buildings, and some trees without leaves in the background (winter). Then in the next scene and those following it is back to summer.
Continuity mistake: When the cat in on the table in the diner, the word "ORION" on the cat's collar is in normal capitalized block lettering. But when the cat is on the table in the morgue, the word "ORION" is in calligraphy. Also, the colour of the cat's collar seems to change between these two points.
00:42:40 - 01:08:15
Continuity mistake: In the beginning, when K shoots the Mexican-Alien, one of the cops gets covered with blue slime all over his face and hat. Watch the right side of the hat: The length of the slime differs between the front and back shots. It's more seen when the scene is about to end and the slime starts to fall down in the front shot, but stays still in the back one.
Continuity mistake: 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.
00:24:25 - 00:26:35
Other mistake: There is a mistake in the French subtitle translation. In the diner when the cook asks Edgar the Bug, "where's Ivan?" Edgar responds, "[I] gave him a break". The translator writing the subtitles must have thought he was saying "GIVE him a break" because the subtitle reads, "laisse-le tranquille" which means, "leave him alone".
Continuity mistake: After Kay neuralizes Jay the first time, Jay 'wakes' up in a restaurant and Kay hands Jay a card. He tells him to report to that location. The address can be seen written on the back on the bottom edge of the card. Jay flips the card over to read the address and it's still on the bottom edge of the card. When flipped, the address should now be on the top edge of the card.
Continuity mistake: When the Mexican alien is running away, the whole scene is all wrong: He runs for a long time and passes by many bushes and cacti, but when K takes out his gun, the alien is just 10 meters away. Plus, from the POV angle, he passes by the cactus to the left of the guard twice.
Continuity mistake: The MIB applicants are all sitting in the testing room and Zed talks about how they are all the best of the best of the best like, "Rangers, Navy SEALs, NYPD". The only sailor sitting in the room is not a SEAL, he's EOD. You can tell because he is not wearing the Special Warfare badge on his uniform, he's wearing the badge for Explosive Ordnance Disposal.
00:24:35 - 00:27:30
Continuity mistake: When Jay touches the ball that goes flying around, the ball goes past the Immigration Stats board where the time reads 33:01:42 pm. Then when we see the alien surveillance map, the time is 30:21:40 CTN. Then the second shot of the map, the time reads 32:01:42 CTN.
Continuity mistake: In the opening scene, when the van is approaching the road block, you can see the 4 sets of headlights. However, when we see the road block from behind, we see one cop car parked at an angle, in front of another cop car's headlight, which would obstruct the view of the light which we saw before.
Other mistake: Soon after Jay pushes the little red button on the Ford POS, Kay inserts an eight track cassette. If you look at the eight track player, you can read "Select". The car is upside down at this point, but the word "Select" on the player, as well as the title of the cassette, "Elvis 'Promised Land'" are both right-side up. This means that, if the car were right-side up, the text would be upside down, and, in turn, the entire cassette player would be upside down. It is clear that this mistake was made by not paying attention to the orientation of the car as the scene was shot. It is also clear that the shot is done with the camera right-side up since Kay is in the driver's seat, which, right-side up, would be on the left, but since the car is upside down, he's on the right, which is seen when he inserts the tape.
Continuity mistake: During the written test, Hudson accidentally pierces the page with his pencil. He then reverses the pencil so the eraser is towards the paper. After the cut to Jensen trying to work on his, Hudson's pencil is suddenly corrected with the point towards the paper.
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Continuity mistake: At the end of the film, Will Smith and Tommy Lee Jones blast the Bug, getting covered with entrails, intestinal contents, etc. Then in the next scene, when Jones is passing the neurolizer to Smith, they are both clean, while Linda Fiorentino is still covered all over. Absolutely nothing is mentioned in the film that indicates their clothing to have any sort of extraordinary qualities, which would make their garments unique.
Continuity mistake: After Laurel is abducted and Jay tries to find her in one of the cabs, Kay brings the LTD around to pick Jay up. The LTD stops beside Jay in a position parallel to the white lines in the road. Jay gets into the LTD and when Kay drives off the LTD has noticeably changed its angle to the white lines even before it begins to move.
Revealing mistake: When James Edwards (later, J) catches the alien in the beginning and has him next to a wall, the alien pulls out a "reverberating carbonizer with mutate capacity" to shoot J. A quick tussle, and the alien drops the gun. When the camera goes to a close up on the gun, watch carefully. You see it quickly fade out of view after it comes to rest, and replaced with a few burning sparkle effects to simulate disintegration.
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Continuity mistake: When K and D are talking to Mikey, they are standing in a clearing with no grass on the ground. When Mikey spots the trooper behind him, he turns and starts running towards the trooper, and he is running down a pathway in the grass.When K shoots Mikey and he is blown apart, there is a shot from the trooper's point of view towards K and D, and the pathway that Mikey just ran down is no longer visible and K is no longer standing in a clearing.