Continuity mistake: When Tweety (as a monster) says "You bad old puddy cat!" to Sylvester, you can see that Sylvester has a drawer open in front of him. But when Sylvester falls to pieces in the next shot, the drawer he had opened is now shut and he is now standing in front of an open drawer in the bottom left hand side of the cabinet, and when Sylvester runs off in the next shot, the drawer is closed.
Continuity mistake: When Dr Jekyll enters his laboratory at the start of the cartoon, he locks the door with his key. After drinking the Hyde Formula, he turns into Mr Hyde for a short time before going back to Dr Jekyll. When Jekyll leaves the laboratory, he opens the door without unlocking it.