Continuity mistake: When the brothers go into the attic, there is a large portrait facing away from the walls that it is propped against. They open a box and moths are released. The fat one gets hit by a pole, and wanders across the room. He then appears with his head through the painting. His head would have gone through the painting the other way, as it was facing us, not the wall.
Continuity mistake: In the scene where the mouse is trapped behind the skirting board by the nails fired by the nail gun, we see at least 5 nails, yet on the exterior shot of the same skirting board, where Lee Evans is about to hammer in a protruding nail, we only see 2 nails in the board.