Continuity mistake: When Clayton undresses for Whale for the last time, Whale is watching him in a window reflection. However, the reflection is not flipped as it should be.
Continuity mistake: Whale commits suicide by drowning himself in the pool. When Clayton pulls him out the color of Whale's suit changes from black to brownish, and vice versa when Clayton throws him back in. Varying degrees of wetness should not be the reason as he should be drenched too while he is lying at the poolside. (01:33:40)
Factual error: The supposedly Great War vintage gas mask James Whale finds and later gets Clayton to wear is in fact a British style introduced in the 1930's, and the specific variation shown was not made except during WW2. In addition, during the flashbacks to WW1, various pieces of WW2 equipment crop up (e.g. helmets with spring-loaded canvas covered chin straps instead of leather chin straps, and WW2 British pattern gas mask bags).
Audio problem: When Clayton fights with Whale, who begs him to kill him, he audibly tears his clothes although you don't see any damage. When Whale gets up his clothes are perfectly ok. (01:26:25)
Continuity mistake: The bar where Clayton hangs out has separate windows with small panes from outside, but glass bricks without any partition from inside. (00:31:35)
Continuity mistake: While Clayton sits with Hanna in the kitchen before he has lunch with Whale the clock on the wall switches back and forth between 2:30 and 2:35. (00:43:15)
Continuity mistake: Before Whale has lunch with Clayton he is sitting at a counter opening some letters. There is a glass ashtray on the counter that is about a meter away from the letter pile in all wide shots, but right next it in all close-ups. (00:46:05)
Continuity mistake: Before Clayton poses for Whale for the last time he drops the towel around his waist. When they start to fight and Clayton tries to re-dress the towel is already half back in place. (01:24:55)
Continuity mistake: During the interview at the poolside Whale reaches for a box with cigars. In the next shot his empty hands are resting in his lap, and when the camera angle changes again the already opened box is back in his hands. (00:12:10)
Continuity mistake: When Whale and Clayton smoke cigars after lunch you can tell from the ashes at the tip that Clayton's has burned for at least five minutes the very moment after it was lit, while Whale doesn't get his cigar burning properly throughout the scene (which would be a real shame for an obvious cigar aficionado). (00:49:05)
Continuity mistake: During the interview at the poolside, when Whale makes Kay take off his pants, he is holding his cigar either to his mouth or to the side in alternating shots that follow each other too quickly. (00:14:05)
Continuity mistake: When Whale paints Clayton's portrait for the first time he hangs his shirt on a coat stand behind him. The way the shirt hangs changes between straight and crumpled several times throughout the scene. (00:29:20)
Continuity mistake: When Whale collapses and Kay takes him to the atelier you see Hanna come running with all his medicine tucked in her apron. When she arrives he is already rested on his bed, not possible the way he was dragging his feet. (00:15:45)
Continuity mistake: In the scene when Whale paints Clayton while a thunderstorm is raging outside a pen in Whale's hand appears and disappears a number of times. (01:19:30)
Factual error: Brendan Fraser's gelled-up haircut fits very much the time when the movie was made but not the time when it was set, i.e. the fifties.
Continuity mistake: While Clayton is having lunch with Whale his water glass is either full or two-thirds full depending on the camera angle. (00:47:45)
Revealing mistake: After Whale compliments Clayton for the marvellous shape of his head, Clayton pulls faces at himself in the side mirror of his pick-up before he drives off. Considering that the camera is positioned at hip level and we see his face in the mirror he couldn't actually see himself. (00:24:40)
Revealing mistake: In the last scene of the movie Clayton steps of the house and it starts raining. The first rain comes down diagonally in a big gush like from a watering can. (01:36:50)
Continuity mistake: Before it starts raining at the party in Princess Margaret's honor the ground is wet already. (01:13:00)
Continuity mistake: When young Mr. Kay is interviewing James Whale at the poolside Hanna brings some ice tea and two glasses on a tray. She puts the tray down and lays out the place mats. Then she reaches for the first glass, and when she puts it down in front of Kay the other glass is already standing in front of Whale. (00:09:55)
