Continuity mistake: When the Wolf runs to the cabin, the front door is initially made of wood. But when the Wolf opens all the doors and finds McPoodle waiting for him, the front door now has molding on it.
Continuity mistake: When Charlie Brown is talking to Lucy at her Psychiatrist booth, the sign says "The Doctor is Real In" or "The Doctor is In" depending on the viewing angle.
Continuity mistake: Geri (with glasses) knocks off the box of chess pieces after faking a heart attack, but when the camera pulls back at the end of the movie, you can see there is no chess box or pieces on the ground.