Continuity mistake: In the beginning scene where Brian is telling his sad story to the bartender at the bar, he pulls out a picture of him, Jacob, and Anna. Then the movie progresses to a sequence of their childhood, and then focuses back in on the picture. The two photos are different. One is a close up of the three kids' heads; the other is taken from much farther away.
Continuity mistake: In the scene in the karaoke shop, watch the light through the window. Sometimes it's daylight outside, sometimes it's dark.
Continuity mistake: In the next scene between the rabbi and priest on the temple's steps, watch the bad edit cuts back and forth between them (when one's talking, and shot from behind his head you can see his lips are not moving).
Continuity mistake: The two men are talking on the street while waiting to cross the street. Watch the kids around them. The two girls on the left bottom look right at the camera. Another girl towards the mid-right, is just mumbling out words. If you look at her lips, you can tell that those are not words.
Other mistake: When Brian and Jake are sitting against the fence just after being beaten at basketball, Jake asks why Anna called Brian and not him. Brian yells "What are you, in the eighth grade still? Fynn before Shram." When he says "Fynn" which is his surname, he points at Jake, and when he says "Shram," Jake's surname, he points at himself.
Continuity mistake: In the scene where Anna is over at Jake's and Brian is coming up the stairs to go to the Karaoke place with Jake, you notice it's light outside. When they get to the Karaoke place it's dark.
Continuity mistake: In the scene when the priest goes to Elfman's apartment, watch for the fishpole microphone to drop down into the scene.
Continuity mistake: In the scene where the priest is going over to Jakob's apartment its morning and he says to Jakob we have to go the karaoke place closes in 20mins. How can that be when it takes time to get there and they were there for a fair amount of time?
Factual error: Prior to the Yom Kippur sermon where Rabbi Stiller is asking for forgiveness for not revealing his relationship, the cantor sing the Kol Nidrei prayer, which is only sung once a year on Yom Kippur eve. Totally obvious mistake to anyone who knows anything about Judaism. Clearly Stiller and the script writers do not.