Revealing mistake: One of the accountants' computers has no power cord attached to it.
Revealing mistake: When walking across a curved path, you can see Judy step off the floor where he was supposed to walk.
Revealing mistake: When Gypsy tries to hit Helen with her weapon, she misses and hits a table instead, causing one of its leg to break off. However before the weapon even hits the table you can see the leg coming off from the table; obviously being pulled off.