Continuity mistake: When Brennan rubs his nuts on Dale's drums, Dale comes in and starts fighting with him. Brennan doesn't have a chance to put "them" away but in the next shot his zipper is up.
Continuity mistake: When Dale tells Brennan he needs to hear him sing, Brennan has a sword and is swinging it around. After he sings, he gets up and the sword is shown on the floor in its scabbard. They flash to Brennan, then back to Dale and the sword is gone.
Suggested correction: He places it down before sitting on the bed to sing.
Continuity mistake: The bottle of ketchup in the dinner table scene, early in the movie, alternates from right side up to upside down, from shot to shot. (00:08:45)
Continuity mistake: In the scene where Alice spells words with her food on her dinner plate asking to have sex, the very next view of her shows a smaller plate in front of her.
Continuity mistake: When Brennan and Dale first meet on the front lawn, they stand and stare at each other for a while. With every shot change, it continues to change from either being sunny or shadowy in the spot where Brennan stands. (00:07:00)
Continuity mistake: In the christmas scene where they are decorating the tree, we see Robert eating a christmas-tree shaped biscuit. When he gets up, the biscuit is suddenly larger and more whole than before, where it was almost finished. (00:57:45)
Continuity mistake: In the scene of the step brothers' first dinner together, Will Ferrell can be seen picking up a French fry, but in the next shot he is holding a half eaten chicken nugget. (00:08:30)
Continuity mistake: When Dale and Brennan are fighting over the drum kit, Brennan throws Dale into the gong and it falls over. In the next shot it is standing again. (00:18:15)
Continuity mistake: After the first dinner scene with the family, Dale finally decides to leave and head upstairs. He places his napkin down next to his plate. In the next shot it has vanished. It then reappears a few shots later. (00:10:15)
Continuity mistake: At the Catalina Wine Mixer, Brennan Huff's voice breaks the large glass/ice helicopter sculpture. A few moments later, his step father is clapping and the helicopter sculpture is visible behind him. (01:22:45)
Continuity mistake: When Brennan and Dale are in the tree house and Brennan's brother comes up, Brennan has a magazine in his hand, and each time the shot changes, he doesn't. It alternates between the two. (00:27:55)
Continuity mistake: Near the start when Nancy and Robert first meet and are undressing themselves, Robert removes his jacket in a wideshot and his shirt and tie are still on. But in the next closeup the tie has vanished and he is suddenly unbuttoning his shirt. (00:02:10)
Continuity mistake: When Brennan and Dale are in the tree house and Derek comes up to talk to them, the soda can over Derek's shoulder moves around between shots. (00:27:15)
Continuity mistake: In the dinner scene where Derek is over, he is telling a story to Robert about fishing. During the whole scene if you watch Alice who is sitting beside Derek, her wine glass repeatedly jumps from her hands to back on the table instantly. (00:24:50)
Continuity mistake: When Dale is questioning Brennan as to why he is sweaty, and again when he comes downstairs after examining his drum kit, the remote control Brennan has swaps which hand it is in a few times and his hands keep switching their position too. (00:16:45)
Continuity mistake: When Brennan and Dale are watching TV, there's a blue can of Pepsi on a table, but in the next shot the blue can disappears from the table.
Continuity mistake: After arriving to the new house, Brennan is seen in the car as Nancy and Robert talk to the neighbor (Don). Brennan's arm is seen up holding the handle on the interior of the car near the window then down between each shot. (00:06:05)
Continuity mistake: In the scene with the bullies, as the bullies are approaching and one says, "Hey, fag stick," Dale and Brennan are stationary next to a tree. When he says,"Long time no see," they are moving to the same position again.
Continuity mistake: When being attacked in the schoolyard, Dale and Brennan are in a different position relative to the big tree whenever the camera angle changes.
Continuity mistake: When Nancy and Robert find the kitchen in a mess, after Brennan and Dale's sleepwalking episode, the mess on the floor and counter differs between shots. (00:22:00)
