Continuity mistake: In the episode when Penny went to work with her mom and the Magician comes in with the tiger that is acting strangely. The tiger is sitting on the floor and has just eaten its food. Penny is standing there next to the tiger, the camera goes to her mom for about two seconds, then it goes back on her and the food has returned in the bowl again. Then it's empty again.
Revealing mistake: At one point when Alan's phone rings (Nokia 8310) he answers it and talks to the caller yet it's obvious he isn't talking to anyone. He blatantly presses the red/cancel button to answer the call. The image hadn't been reversed though, because he pressed the exact same button to end the call.