Continuity mistake: As they are escorted out of the Mar Vista rest home, Jake kicks Claude Mulvihill in the stomach and if you look closely his hat never leaves his left hand as he smashes his head into the front railing. In the next shot as Claude drops his gun to the floor we see the hat on the ground next to it. (01:19:10)
Revealing mistake: When Gittes visits the orange grove and crashes into the tree, you can see that a steel plate has been placed around the tree to protect it.
Continuity mistake: At Ida Sessions' house, Lieutenant Escobar shows Jake his phone number on the wall above her phone. In the close-up of the phone number there's a card stuck in between the wall and the phone and if you look closely the left edge is frayed. When Jake walked into the room it wasn't. (01:41:00)
Continuity mistake: As Evelyn Mulwray stands in front of Jake at the table in the restaurant, look closely at the red chair behind them. When she first walks in, the seam is under the wood post in the center of the screen. In the next shot, it's been moved about two feet to the left. (00:45:50)