The One With The Hypnosis Tape - S3-E18
Continuity mistake: When Pete is trying to ask Monica out at the diner she works at, she rejects him while placing the bell jar over the cheesecake and the pie server on the counter. In the next shot, the bell jar is nowhere to be seen and the pie server is up on the cake stand with less cheesecake. Then the bell jar reappears over the cheesecake. (00:07:00)