Factual error: In an attempt to create a believable 1940s gym, it appears the production crew got hold of many contemporary boxing posters as possible. Most of these were Greeked to avoid mentioning real boxers (such as "Dave Ritlaf" and "John Paropianeo"), but one of these prominently features a "Ronnie Harris", along with a photograph. Ronnie Harris was a real boxer, but wasn't even born until 1948, 7 years after this scene was set, giving away that a poster from the '70s was used. (00:16:08)
Visible crew/equipment: When Jake is in the bedroom with his wife (where he pours ice water on himself to calm down) you can see the top of some crew member's head in the foreground right below the camera lens.
Continuity mistake: In the first scene with De Niro's first wife as Pesci arrives, he is improvising as he argues with her and he says "you call those carrots" and she says "you ate them didn't you". He replies "I got no choice". But he had flipped over the table in the prior scene as she was serving the carrots so he never even tasted them.
Continuity mistake: In the scene when Robert De Niro asks Joe Pesci to punch him, you can see blood on De Niro's face at one point. Then you in the next shot of De Niro, there is no blood on his face.
Continuity mistake: When Joey and Sal are walking down the street, they come up to one apartment where people are standing outside talking. Just before that the blind in the window behind them is up, but in the next shot it's down.
Continuity mistake: When Joe Pesci has to apologize and shake hands with the guy he got into a fight with, there is one shot of him shaking hands. The very next shot - with no transition whatsoever - shows Joe Pesci holding/playing with what appears to be a matchbook.
Continuity mistake: Early in the film there is a scene, clearly an improvisation, where De Niro's character is courting his future wife. They are sitting across from each other at a small dining table in an apartment. Apparently the director has told De Niro nothing more than "try to get her to sit on your lap", which is accomplished so quickly and easily that he looks at the camera, obviously expecting to hear "cut!" or get some further suggestion. Nothing happens, and De Niro, momentarily at a loss, tries to come up with more action, a kiss, or something. He quickly succeeds at this as well, and looks at the camera again! The scene still is not cut, and continues to unravel.
Revealing mistake: In the scene where Jake fights in Cleveland, in one shot right before he punches you can see his opponent's mouthpiece is taped to his head so it will fall off making it look like it came out of his mouth. In the next shot he has his mouthpiece back in his mouth.
Continuity mistake: There is a scene in the film where De Niro and Pesci are in a living room and De Niro is next to the TV trying to fix antenna whilst talking to Pesci. In most of the camera shots between the two guys the antenna often changes position without De Niro moving it.
Continuity mistake: During a scene where the boxer is in his home, you hear an ambulance siren from his window. The siren is a modern siren rather than the slow low to loud sound then back from loud to low type when the movie was dated.
Chosen answer: No. But Jake's paranoia and possessiveness had consumed him to such a degree that he was convinced that he (Joey) had, based on Vickie's impulsive remarks.