Revealing mistake: During the scene when Fletcher pummels himself in the courthouse restroom, the walls shake when he throws himself against them. The restroom walls were some type of marble or granite, and in real life would be very thick and rigid, making it very obvious this was a movie set.
Revealing mistake: In the scene where Fletcher drives out of the parking garage almost causing a car accident, you can tell it's his stunt double, because his stunt double is wearing sunglasses and doesn't look too much like Jim Carrey. Then it shows a back view of Fletcher speeding away and his sunglasses are gone.
Revealing mistake: In one scene, when Fletcher has the curse and he cannot lie, he's running away from everyone. Then the lift door opens and his boss comes out and she calls him, Fletcher runs away and takes the emergency exits stairway. Just before the door closes after him he bumps into the wall, and it shakes really hard.
Revealing mistake: At the end of the movie when Max is getting ready to blow out the candles, the shadow on the wall behind the mom comes from a light source that's equal in height to Audrey. Since the candles are the only light source in the room the angle they would cast would be more towards the ceiling.