Continuity mistake: In the pilot episode, the guy Rachel left at the altar is called Barry Finkle. In all the other episodes his name is Barry Farber.
The One With Joey's Porsche - S6-E5
Revealing mistake: The triplets are supposed to be two girls and a boy; however, certain revealing shots of their anatomy when they are in Monica's apartment show that the two babies playing the girls are actually boys.
The One Where Joey Dates Rachel - S8-E12
Visible crew/equipment: When Ross is wearing roller-blades while teaching his class, just as he points to the map and says, "Here," the second time, there's a hidden crew member that can be seen behind the end of the set wall with the map, at the left side of the screen.
The One With Phoebe's Wedding - S10-E12
Continuity mistake: When Monica and Phoebe are talking about having a harpist versus Marjorie playing the steel drums, the handbag strap over Monica's shoulder vanishes and reappears.
The One With Phoebe's Birthday Dinner - S9-E5
Continuity mistake: Phoebe implies that her birthday is round about Halloween - October 31st. However, in The One With Frank Jr in series three, she tells Frank that her birthday is February 16th. (00:00:05)
The One with All the Poker - S1-E18
Visible crew/equipment: The friends are all at Ross' place. Marcel (the monkey) is dancing to the music just before they all play poker (before Rachel enters). However, the reflection of the animal trainer directing Marcel is visible in the TV screen. (00:11:45)
The One After Joey And Rachel Kiss - S10-E1
Visible crew/equipment: After Chandler starts removing Monica's braids from the shower curtain rings, when it cuts to Joey and Rachel walking into their apartment, we can see the hole in the wall at the right side of the screen. And it's seen again when Ross walks in on Rachel and Joey kissing.
The One Where Rosita Dies - S7-E13
Visible crew/equipment: When Joey sits on the Lazy Boy chair Rachel purchases, there are a pair of denim jeans seen behind him - the crew member steps back out of frame but can still be seen.
The One Where Emma Cries - S9-E2
Continuity mistake: In the coffee house, when Ross and Joey are having a fight about Joey's proposal to Rachel, Ross does the "quote gesture" with his hands and Joey says he doesn't know what this means. In TOW the Secret Closet, Joey used it himself when talking to Chandler, in the scene where he asks him to bring a bobby pin to pick the closet's lock. (00:08:55)
Continuity mistake: Mr Heckles's apartment number changes from 8 to 5.
The One with the Dozen Lasagnas - S1-E12
Visible crew/equipment: When Rachel's dumping all of Paolo's clothes over the side of the balcony, we can see the apartment's back wall is only half a wall, with the sound stage and equipment at the left side of the screen.
The One With The Red Sweater - S8-E2
Plot hole: They say that whoever the sweater belongs to left it behind, but in The One Where Rachel Finds Out that Ross videotaped them together it is clear that Ross is not wearing anything under the sweater, therefore for Ross to have left it behind he must have gone home topless.
The One Where Ross Is Fine - S10-E2
Factual error: If Ross really was holding the sizzling fajitas like that for as long as he was without any gloves, he would be in the emergency room.
Revealing mistake: When everyone leaves the apartment together for the last time, they show Chandler and Monica with the twins in the stroller, and you can tell they are dolls.
The One With The Prom Video - S2-E14
Visible crew/equipment: After Chandler throws the basketball and breaks the lamp, in the next shot of Joey as he mentions the bracelet, we can see the reflection of a crewmember (standing behind the foosball table) on the left side of the TV screen (Chandler's reflection is at the center of the screen).
The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: While "The Dick Van Dyke Show" is playing on TV, when Rachel walks in and heads over to Ross, a crewmember can be seen at the left side of the screen, behind Phoebe.
The One With All The Haste - S4-E19
Visible crew/equipment: After Joey convinces Chandler to agree to the bet, when Phoebe walks over to the recliners and tells everyone that she has a game, the camera can be seen moving at the right side of the screen. (DVD).
The One With The Fake Party - S4-E16
Visible crew/equipment: While Rachel is talking to Chandler she tries to get Joshua's attention so she pretends to laugh, and in the shot facing Joshua the end of the set wall can be seen, with the brick set wall from Central Perk on the other side.
The One With All The Rugby - S4-E15
Continuity mistake: During the rugby game, when Ross tells Phoebe and Joey that he thinks he's dying there are two hairsticks in Phoebe's bun in the shots facing her, but there's only one hairstick in her bun in the shots facing Ross.
The One With Joey's Dirty Day - S4-E14
Visible crew/equipment: After the exterior shot of Bloomingdale's, when it cuts to Rachel helping Joshua with his clothes the camera can be seen at the left side of the screen.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.