The One With Mac & C.H.E.E.S.E. - S6-E20
Continuity mistake: In the episode before, Rachel's hair is just underneath her shoulders. Then, a few weeks later when Ross gets back from Spring Break, it's a lot longer than before.
Continuity mistake: When Joey and Chandler talk about how to tell Monica that it is too soon for marriage, Joey fills his plate up with scrambled eggs. When he walks over and sits at the table, the eggs appear smaller on his plate. (00:15:54)
The One Where Chandler Can't Cry - S6-E14
Continuity mistake: In the beginning of the episode when Joey tells Chandler that he hasn't forgiven him for kissing one of his sisters, Monica and Chandler's TV, entertainment set and ferns are missing from the set and there are cables protruding from the wall. The area is completely bare except for the French poster. Everything's back to normal slightly later in the episode.
The One Where Paul's The Man - S6-E22
Continuity mistake: In the opening scene in Central Perk when Paul (Elizabeth's dad) takes Ross to one side to talk to him you can see the girl in the blue top enters the door twice: first the shot after Paul says "I'm funny like that" and then again after Ross says "I realise it upsets you".
The One Where Ross Got High - S6-E9
Continuity mistake: When Rachel tells Phoebe that she's making a traditional English trifle, Monica's holding a cloth napkin, but in the next shot the napkin's suddenly gone and she's now holding forks.
The One Where Ross Got High - S6-E9
Continuity mistake: When Phoebe finishes telling Rachel about her thanksgiving dream about Jack, Chandler is looking straight ahead with his arms crossed. Cut to the next shot when Jack and Judy are coming out of Monica and Chandler's room, and his arms are immediately uncrossed and he's looking at the women. (00:20:05)
The One With The Joke - S6-E12
Continuity mistake: In the coffee house scene when Joey reveals that he is working there, the strap on Joey's apron goes back and forth from being twisted around his neck and then straightened out. (00:10:50 - 00:12:50)
The One With The Apothecary Table - S6-E11
Continuity mistake: When Phoebe and Rachel are first talking about the apothecary table, there are two piles of CDs on it. In the side shot you can see that the two CDs on the top of the pile in front of Rachel are overhanging by a few centimetres. A few shots later, however, the top two CDs are overhanging on a different side. (00:06:05)
The One With The Apothecary Table - S6-E11
Continuity mistake: When Phoebe and Ross are talking about Ross buying his sheets at the flea market, Phoebe says, "Ross, come on, you gotta loosen the purse strings a little" with her hands by her side. The camera cuts and her hands are now out in front of her.
Continuity mistake: The white dog that Joey gives Chandler sometimes has red lips and sometimes does not.
The One That Could Have Been, part 2 - S6-E16
Continuity mistake: When Chandler goes into Monica's apartment after he beeps Dr Roger for a "ruptured spleen" his hair is sticking up through the front of his cap. After he tells Monica "You should be with me", the shot goes to Monica and when it goes back to him, his hair is neatly tucked into the cap.
The One With The Proposal, part 2 - S6-E25
Continuity mistake: Right after Monica says, "You wanted it to be a surprise", the camera pans to Joey who shuts the door firmly, however in the next shot you can see the door gliding back open and then shutting again. (00:18:40)
The One With The Joke - S6-E12
Continuity mistake: In the scene in the coffee shop where Joey tells his friends about him closing down the coffee shop when he went to the audition, as Rachel says "He left work in the middle of the day to do a personal errand?" two men walk past behind the group. As she continues talking just a few moments later, the same exact men walk past again.
The One Where Ross Meets Elizabeth's Dad - S6-E21
Continuity mistake: When Chandler is about to put the toilet paper on the table, the picture with the little girl is facing Phoebe. In the next shot, the picture is facing Chandler. Two shots later, it's facing Phoebe again, and then Chandler again in the next shot. (00:08:15)
The One With Mac & C.H.E.E.S.E. - S6-E20
Continuity mistake: As Chandler is writing on the board to remind himself about Joey's audition, the door opens as he's writing "Joey", and there are a bunch of squiggly lines under the y. As Chandler is thinking back at that moment and it moves to present tense, he looks over to the board, and the squiggly lines are different.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.