Continuity mistake: When J is being swallowed by the fish, the floor around him swaps from very dirty, to slightly dirty, to spotless between shots. (00:16:15)
Continuity mistake: When J is in the car with young K, about to head for the bowling alley, the way J holds the matchbox changes between shots. (00:49:55)
Continuity mistake: As soon as Boris blasts the door down, there are guards on the grounds and guards behind some of the cells in the background. After Boris blasts the the steel wall, the guards on the grounds are sucked into the vacuum of space, but the guards hiding in the cells in the background have vanished completely. They certainly weren't sucked into the vacuum of space because they were protected by both the cell bars and the ceiling above them. (00:04:50)
Continuity mistake: As J pops his head up on the tall building, there are windows immediately behind on his right and left and both are closed. The camera pulls up and back to show the scale of the building, then cuts back down to J. Now suddenly the window on his right side is open, and the lamp in the room is on. The window also changes from closed to open a few times in this scene. (00:33:25)
Continuity mistake: In the last scene at the diner, the various camera angles show the background characters. The view to Will Smith's right shows 5-6 empty seats down to a man at the end of the counter. When Smith and Jones leave, the camera pans left down the same seats and there is Griff sitting 2 stools away from Will's spot. He wasn't there 10 seconds earlier and has partially eaten food in front of him, indicating he was there for a while. And you think Will would have noticed him there after all they recently went through.
Continuity mistake: When K returns to the diner to leave the tip, he places down the money with his left hand and his finger is still on it as the shot ends. As it cuts to the next shot he is suddenly pulling his right hand away from the money. (01:37:40)
Continuity mistake: As J is telling K the truth about Boris killing him at the Moon Launch, one shot from behind K shows his head is down. The next shot, he is suddenly looking straight forward as he punches J in the face. (01:16:15)
Continuity mistake: When they arrive at the ball park, K gives J his stuff back. The close up of the time device in J's right hand shows his thumb is closed in close to his hand. But the shot cuts to show both him and K, and suddenly his thumb is stretched out. K also puts his arms down twice during this part. (01:06:10)
Continuity mistake: At the diner, K asks J if he has a girl in the future. In that shot, J is looking down at his food. It cuts to a different angle and J is instantly looking straight forward as he is turning his head to K to say "I got you." (01:05:05)
Continuity mistake: At the diner, K says the "pie don't work unless you let it." J then looks at him and begins waving his fork at his own pie, but the shot cuts to a different angle and J is instantly looking down at his pie as he begins waving his fork. (01:03:50)
Continuity mistake: When Griffin is telling J that his buddy might give him antacids for his gastric distress, there is a small group of people behind him. One of them is wearing a picnic cloth style dress with red and white squares as the pattern. She walks away to the left of the screen, but then it cuts to a close up of Griffin as he says "But that depends" and she is suddenly right behind him. (00:58:50)
Continuity mistake: When J is in his lying fest at the 60's MiB headquarters, he starts calling two guys that walk past him "K." The first one walking by has a clipboard he is working on. He walks totally past J, and then another guy with nothing in his hands begins walking by and is almost passed J. Then the camera cuts to a close up of J, and the second guy passing him suddenly has stuff in his hand he is working on. (00:43:45)
Continuity mistake: As K is questioning J in the past at the MiB headquarters, there is a green alien behind J talking on the phone. In the close up of J as he's telling K to turn the power down on his tazer, and he can't feel his tongue, the MiB agent behind J is seen taking the phone from the alien and hanging it up. It cuts to K saying "How do you know my name?" then back to J in a shot further away. The green alien is seen handing the phone to the MiB agent again to be hung up. (00:43:35)
Continuity mistake: After the timeline is altered, J returns to MiB headquarters where he is met by Agent Double A in the elevator. After a brief monologue by Double A, J turns to him and says "Give me 5 feet, or I am gonna pluck you in your throat." He holds up his hand like he is going to flick Double A. In one shot, his wrist is bent up, but in the next shot, it's bent down. (00:26:20)
Continuity mistake: Jeffrey begins giving J a quick crash course on how to use the Time Jump device on top of the building. Just before he says "When you're moving fast enough" he pats J on the back, receiving an angry look from J. Jeff then puts his arms down as J begins slowly moving forward. The camera then cuts to a closer shot as he begins that line, and suddenly Jeff's arm is back on J's back, and J's arms are in a different position. (00:34:25)
Continuity mistake: Trying to crush the metal tray that J wedged in its mouth, the large alien fish breaks a tooth on the tray. J then picks up a couple of bottles of mustard and squirts its nostrils full. During that shot, the shape of the broken tooth has changed slightly, and the remaining piece is larger. (00:16:25)
Continuity mistake: Just before K says the line "I used to play a game with my dad..." at Wu's restaurant, he is looking straight forward. But as he begins saying that line, preceeding a sigh, the camera cuts to a different angle and suddenly he is looking to his right. (00:13:45)
Continuity mistake: When K slaps Wu with the Spikey Bulba the first time, you see Wu's head turn to the right as he's hit from the over the shoulder view. But when it cuts to show Wu's face, his head is suddenly being thrown back rather than turning right. (00:12:40)
Continuity mistake: When Boris shoots spikes at the door that K and J are holding, one of them gets stabbed on the upper part of the glass. When the angle changes it's stuck on the center part. (00:17:40)
Continuity mistake: When J puts a tray in the fish's mouth, it swaps from perfect to wrinkled between the first two shots in a time-frame. For the rest of the scene, there's no continuity between the shape it has in the wide angles and in the close-ups. (00:16:20)
Chosen answer: The gold saucer crashed in middle of the street was the ship Boris stole to get to earth. While they are in the restaurant Kay gets a call that tells him a ship was taken from lunar max and it was Boris who took it.