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.
Continuity mistake: When we first see the "They" flag on Yosemite Sam's fort, it is completely fine. When Sam says "Ahoy, there!" there is now a hole in the top right hand corner.