Other mistake: At the end when the naked but invisible hero runs from the police but is given away by his footprints in the snow, the footprints are of shoes, not bare feet.
The Invisible Man (1933)
1 other mistake
Directed by: James Whale
Starring: Claude Rains, Henry Travers, Gloria Stuart, William Harrigan
Revealing mistake: When Jack steals the bike he's supposedly riding it but you can see a rail on the ground.
The Invisible Man: The drugs I took seemed to light up my brain. Suddenly I realised the power I held, the power to rule, to make the world grovel at my feet.
Trivia: A purely technical error with all "invisible man/woman/boy" movies is that the eye works by interacting with light incident upon the retina. The Invisible Man is made so by being rendered transparent to visible light. This means that his eyes no longer interact with light - so he ought to be completely blind. (However, a healthy suspension of disbelief makes for a great story.).