The One With Ross's Thing - S3-E23
Revealing mistake: When the car catches fire you can see that the fire is not in the car but behind the car. (00:05:00)
The One With Ross's Thing - S3-E23
Other mistake: When Ross goes to see Guru Saj, he has his 'thing' removed. However, it is really obvious that Guru is not going anywhere near the thing, because you can see that Ross' shirt is still tucked into his trousers, and the Guru just rubs his hands along the shirt. (00:16:35)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.