Continuity mistake: When the construction worker hits Bugs in the face with a crossbeam, you can see that the worker has paint on his face, but when he goes down the stairs lighting a cigar, the paint has disappeared.
Continuity mistake: When the construction worker digs up Bugs' home with a crane, Bugs emerges from the hole and you can see that there is earth around it, but in the next shot the earth has changed to grass.
Continuity mistake: During the seesaw of bricks gag, Bugs takes off one brick, leaving two remaining. After the worker takes off some more clothes, we return to Bugs, and there is now only one brick left.
Continuity mistake: When Bugs arrives on the 103rd floor, he sees the worker on a large plank of wood with some bricks on the other side. The amount of bricks changes between shots.
Continuity mistake: When the construction worker sees a bird in front of him, he says "Ha!" The worker then sees the city below and falls. At this point, you can see the worker is holding his hat in his left hand, but when he falls through the first plank of wood, the hat is nowhere to be seen.