Continuity mistake: When Jordan slides on the floor going under the closing door her hat goes off landing straight, and already beyond the door. When it cuts to her picking it up it lies on its side and is now on the other side of the door, for her to reach under and collect it.
Other mistake: When the Janitor plays with Kelso 'double or nothing' for tossing the cotton ball a second time in the jar, Todd tells Kelso he now owes him $600, in the end it was $700. This isn't a 'double or nothing' amount of money the Janitor could generate. They started with $5, so the count would be 5 - 10 - 20 - 40 - 80 - 160 - 320 - 640 - 1280 and so on.