Deliberate mistake: When Betty falls in the traphole, Maxine is right behind her, yet when the angle changes she's not only in front, but has turned 180ยบ. This allows for a funnier gag, but is still a mistake.
Deliberate mistake: Though the loose ferris wheel keeps rolling for over a mile, the guys seated on it remain in the same position all the time instead of rolling down and getting crushed by it. Furthermore, they disappear in the wide shots and the wheel appears empty.
Deliberate mistake: A piece of food lands on a soldier's soap and splashes on him. When the angle rises his glasses are covered in soup. The lenses are very obviously painted, for the splash was way to small to produce such mess.