Black Magic Bloopers!
One blooper in Black Magic (aka Meeting at Midnight) that may just be plain laziness on Sidney Toler's part occurs in the basement.
He is supposed to be manipulating a skeleton back and forth on a wire. His hand doesn't match what he's trying to do: Toler grasps the wire and moves his hand back and forth instead of pulling it forward, releasing the wire to grasp in a different place to continue pulling it forward.
The murderer is quite talented in this movie. When he has lured Justine onto an office roof downtown, he calls her to come forward so she'll walk up to the edge of the roof and then off (a la suicide). One problem is he has to be calling her from the roof across the street if she has to come toward the edge of the roof to reach him. If he has to call loud enough for her to hear him across the street, why didn't anyone down on the street hear the murderer?
The last one is from Robert S.:
...when Charlie is in the police department explaining how he is psychic, and the handkerchief dances above his head, take a close look behind him and you can see the lever going that the prop man is using to make the handkerchief jump. That's as bad a blooper as the scrim in the original Dracula!