Continuity mistake: Selina grabs some stuffed animals and throws them in the sink, where she starts jamming a monkey down the garborator. We cut to her face, and when we cut back to the sink, all the other stuffed animals are gone, but we know she hasn't had a chance to shred them because she is still shredding the last of the monkey.
Revealing mistake: Catwoman breaks into the department store to blow it up. She punches her fingers through a metal access panel to get to the gas lines. Look closely at the panel - the holes are already in place at the exact locations where she punches through, they're just covered with white paint or putty. (00:55:15)
Revealing mistake: In the final scene where the Penguin's corpse is dragged in the water by the other penguins, as he's immersed in, a sort of black mat floats away from the body, which was used to make the body drag easily.