When Phoebe, in the coffee house, is talking about the time she stabbed a cop, the shots switch back and forth between her holding a pencil, a coffee mug, and both objects.
When Monica and Chandler run out the room when they hear Joey coming in with Cynthia, they kick a couple of the pillows, but when Joey and Cynthia are looking at the lay-out of candles, pillows and the video camera, the pillows are back in their original position.
After Phoebe yells "he stabbed me first!", the camera quickly cuts to a wider shot of the gang, and Phoebe's mouth says "first!" again with no audio.
When Ross screams "My sandwich," a building is shown to imply that it is the museum in which Ross works and then some birds in a park are shown flying away to imply that Ross's voice caused this. The building is the Alexander Hamilton U.S. Custom House and the park is Madison Square Park, which is about three miles away from the Custom House.