Continuity mistake: In the scene where Renfield is locked up in the sanitarium cell, the camera first zooms in to the horizontal bars on his window. Some shots later, the camera shows the guard looking under the doorflap, and since the door is opposite the window, the shadow of the bars fall on it. The bars have suddenly changed to a criss-cross pattern.
Continuity mistake: At the end of Dracula's dance with Mina in the ball, as he is about to shatter the mirror which has given himself away, he throws a table at it. Mina is shocked, but as the camera shot changes to one of the mirror and the table approaching it, we can see that Mina is looking perfectly calm.