Continuity mistake: During Inspector Kemp's visit at the Frankenstein manor, Frankenstein is playing darts while he is having his conversation with Kemp. He throws the first dart at the bottom 10, but by the time he throws the second dart at 7, the first dart he threw at 10 is now at the bottom of 18. (00:56:20)
Continuity mistake: When Frankenstein releases the monster from the experiment bed, he reaches for the third bar (over the monster's thighs) first, but the fourth bar (over his lower legs) is already open. All of them were closed when they left the monster in the lab. (00:46:50 - 00:53:55)
Continuity mistake: At the castle, Dr. Frankenstein throws darts while talking with Inspector Kemp. The shot of the darts hitting the board does not match with the shot where Inspector Kemp takes the darts back from the board. (00:58:50)
Continuity mistake: During the scene where the blind man, Gene Hackman, is serving soup to the monster, the blind man spills 2 large ladles of soup onto the monster's lap. The blind man then burns the monster by lighting his thumb, thinking it's a cigar. The monster screams, and breaks through the front door, leaving the blind man's cottage. When the monster leaves the cottage, there is no sign of the spilled soup on his clothes. (01:08:50 - 01:10:55)
Continuity mistake: While playing darts at the castle, Inspector Kemp upsets Dr. Frankenstein by talking about the possibility that he has created another monster. This distracts the doctor as he is throwing his five darts (one ends up on the wall, two out the window, one hits a cat, and one is tossed behind his back). But when the inspector's car leaves, there are at least six darts in the tires. (00:59:45 - 01:01:15)
Continuity mistake: When Dr. F climbs up the hay cart, the first wide shot shows him with his waist above the cart. The next shot, from the cart's POV, shows him only shoulder level.
Continuity mistake: When Frau Bluecher is talking to the Monster for the first time, she puts her hand on his head. In a closeup shot of the Monster's face her hand and arm are missing.
Continuity mistake: When the blind man serves soup, there's a spoon in a cube on the left skewed to the right. A couple seconds later it's straight.
Continuity mistake: When the monster sits on the teeter-totter and flings Anne Beesley (Little Girl) through the window, she lands on her bed, head on pillow, eyes closed as if asleep (or knocked out by the landing). When her parents, rushing upstairs, open the door, she is tucked neatly under the covers.
Continuity mistake: The blind man reaches for the cigars, and when the angle changes, half a second later, the broken pieces of the mug have changed position and have also increased and suddenly appear scattered all over the table.
Continuity mistake: As he's about to depart at the train station, Friedrich leans in to try and kiss Elizabeth good-bye. He's mere inches from her nose when the shot cuts, at which point he's suddenly standing more than a foot away from her. (00:16:00)
Continuity mistake: Inspector Kemp is known in the village to have had his right arm to be prosthetic (supposedly torn off by the original monster), but during the searching in the woods scene, after the riot starts, when he signals the villagers to keep quiet, his LEFT arm is suddenly prosthetic. The entire shot was apparently made of the villagers moving from left to right, but the negative was threaded backwards to get them to move from right to left. The Inspector's eyepatch is also on the wrong eye, and a villager is holding his shotgun left-handed (shown at the town gathering at the start of the riot as being right-handed).
Continuity mistake: Frankie arrives at the door of the blind man, who welcomes him. Then there's a close-up of the monster from a bit far away where you can see his shirt and head as if he were alone; however, a frame later the blind man is right next to him, his head almost touching the monster's.
Suggested correction: It's a running gag: Igor's hump changes sides, Kemp's missing arm and eye change sides.
Brian Katcher
Except that for the whole movie every time Inspector Kemp uses his right arm it keeps making a sound to indicate that it's fake, but he can move his left arm normally, showing that it's his real arm. Not only that but, the moving hump was Marty Feldman's idea. It can't actually be confirmed that Inspector Kemp's prosthetic right being switched to the left for that one scene was part of the gag or not.