The One Where They're Up All Night - S7-E12
Revealing mistake: Just after Ross realises that he and Joey are locked out on the roof, he goes over to the door and tries the handle with some force. That whole part of the set moves - door and walls. (00:03:25)
The One Where They're Up All Night - S7-E12
Revealing mistake: When Chandler is getting a pan out to warm some milk, he successfully pulls the bottom pan out without too much disruption, however, the joke (and entire plot device - to wake Monica up) is to make as much noise as possible so Perry pulls out more pans on purpose and knocks them on the floor. This is quite clear - you can see him grasp the wok and pull it out onto the floor. (00:06:30)
The One Where They're Up All Night - S7-E12
Revealing mistake: When Ross is shimmying down Joey, who is hanging onto the fire escape, you can see in his sleeves there are attachments keeping him in place. (00:20:33)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.