Revealing mistake: When the karate instructor throws the old lady, it’s a stunt double. This is evident because the face briefly changes, and the character’s wrinkles reappear after the fall. (00:43:30)
Revealing mistake: Near the end of the movie, when Malcolm's partner pulls out his gun and Lester shoots him, the bullet hole in the wall appears before the bullet wound in Paul Giamatti's arm.





Answer: I think it's the toilet unclogging. Also, he was probably looking at the diarrhoea she left behind in the toilet bowl.