Revealing mistake: When the leading hitman jumps from the balcony you see him land on a rubber mat.
Revealing mistake: When Austin enters the bathroom at the casino, keep your eyes on the door during the scene - it opens by itself before closing. (00:31:10)
Revealing mistake: During the bedroom scene with Felicity and Fat Bastard you can clearly see the air hose that fills his suit when he rolls over in the bed. (00:49:10)
Revealing mistake: As Kevin is flying off the front porch on the toboggan, you can see the small wheels mounted on the bottom of the sled to aid in its "jump". (00:25:30)
Revealing mistake: Gracie hugs the Russian waitress in order to have a better view of the disc hand-off appear on the monitor. As she raises her left hand that holds the book/camera lens, we see that the digital feed that appears on the monitor stays steady and level, even though she is raising the book/camera lens higher and closer to her face. Obviously the feed that we see on the monitor is not taken from the book/camera lens. (00:04:10)
Revealing mistake: When Peter Parker first discovers he can climb up walls (while in citizen clothing), he tests it out by climbing up a building in an alley. During this scene, you can clearly see his clothes hanging out forwards, indicating that the scene was filmed with him crawling along a floor horizontally. (00:24:50)
Revealing mistake: After the woman is strangled and the people come in trying to find the little kid, the dead woman is clearly seen blinking. (00:11:25)
Revealing mistake: In the final racing scene, when Dominic's car hits the truck and flips in the air, you can clearly see the stunt driver's helmet as the car turns in the air. (01:37:45)
Revealing mistake: The kid in the wheelchair is playing a Game Gear with no game in it.
Revealing mistake: When The Mask is dancing with Tina and he turns her into a human tornado while spinning her around, none of the onlookers in the crowd show the slightest bit of amazement at the impossible feat that just occurred in front of them, indicating that the extras were not directed to react to the special effects.
Revealing mistake: When Loomis shoots the marshal's window out, when he makes a u-turn you can see the tire marks on the road and dirt from previous takes.
Revealing mistake: Near the end when Ace gets into his Cadillac, in the first shot facing the front of the car, there is a protective glass in front of Ace (the same width as the windshield) with the dashboard in between that glass and the windshield. Note the vertical edge of the glass is visible at the right side, and the rearview mirror's sticker on the windshield casts a shadow onto the second glass. During the stunt, the flames on the dashboard are between the glass shield and the windshield, keeping the actor safe from harm. (02:46:05)
Revealing mistake: In the disco scene, the DJ is playing music, but the Pioneer decks and the DJ Mixer are not even turned on, as no lights are showing.
Revealing mistake: At the end when Sullivan is shot in the back while looking out the window, you can see blood come through the front of his shirt, meaning the bullets must have exited his body, yet the window he is standing in front of isn't shattered by the bullets that had passed through him. Also, immediately after this when Jude Law sets up his camera to take photos of Tom Hanks dying, the blood all over the glass is completely gone. The window is clean.
Revealing mistake: Riggs handcuffs himself to the depressed businessman. They jump off the building but they're not handcuffed to each other anymore. They used plastic cuffs which could separate during the stunt in case anything went wrong. They break just as they jump, so they grab each other's hands to stay in contact. After they land the cuffs are attached again. (00:31:00)