The One After Ross Says Rachel - S5-E1
Revealing mistake: When Phoebe phones Emily's step-mother to say she is Ross' doctor, she looks out the window behind Phoebe. The buildings are moving slowly from side to side. (00:04:10)
The One After Ross Says Rachel - S5-E1
Revealing mistake: When Chandler and Monica (and later Joey) are talking on the plane on the way back from London, the little display screen (showing a map of the Atlantic and coastlines) in front of Monica's seat shows the little grey plane indicating their position and direction. The plane is facing east, as though they are travelling towards London, but they are supposed to be flying back to New York. (00:14:45)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.