Danny Madigan states that after the prefix 555, there are only 9999 possible phone numbers, since only four digits are available. This is incorrect: there are 10000 possible phone numbers. He forgets that the combination 0000 is also available.
When we first see Benedict and he fires blindly at the target next to Frank, as the camera zooms in towards him you can see that his revolver has a threaded line holding it up steady for the perfect bullseye shot.
When Danny is watching the movie and the ticket activates, Jack shoots the the dynamite which flies out of the screen and lands in the movie theatre, Danny runs towards the screen to take cover. Later, after Benedict leaves the movie, Jack and Danny follow him and land in the same movie theatre and there is no sign of the explosion that would have resulted from the dynamite.
While in the real world (New York) Jack Slater plays a game of chicken with a taxi. When his car starts going down the alley you can clearly see a cable running across the floor attached to Jack Slater's car.
When Jack falls from the broken elevator, the crane is moved right below him so he can grab on to Leo the Fart. However, you can clearly see that Leo is not attached to the crane, but when the shot changes, Jack grabs on to Leo the Fart's legs.