Continuity mistake: Frank is stabbed in the middle of his stomach, but the wound is on his side.
Continuity mistake: When Bob finds Scott and Kate at his office with the money and runs at them, he slams into a frame at the end of the hall breaking the glass. It cuts to a different angle and suddenly he's slamming into it again but the single sound effect is still playing. (01:14:41)
Answer: A lot of the time with modern comedies, they'll usually do a scene as written, then do a number of improv takes where the actors and director come up with jokes on the fly. Then in editing, they'll pick the (presumably) best bits from both the scripted and improv takes to put into the finished film. And Will Ferrell confirmed that there was indeed a lot of improvising on-set of "The House." Unfortunately, without a copy of the shooting script, it's basically impossible to tell exactly how much of the finished film is made up of the unscripted improv. But it's fair to say that at least a decent chunk of the movie was made up of improv comedy. So chances are it's not just you.
TedStixon