The dog statue on the balcony points towards the window when inside the apartment, but when Phoebe was out on the balcony the dog was pointing in the opposite direction.
When Phoebe and Joey are holding the wishbone, the position of Joey's thumb changes between shots.
When Chandler is on the phone with Charlie the second time, he hangs up the phone twice. Once in the close up, and then again immediately in the wide shot.