When the gang are in disguise, Shaggy & Scooby are hiding inside bins. Despite the bins saying 'push' on the lid, they are proved to not be push bins when Shaggy looks out lifting the lid up.
Velma tells Shaggy to put his put his hands at 10 and 2 "just like the DMV recommends", but earlier in the scene Fred establishes that they are in Ohio which has the Bureau of Motor Vehicles (BMV) instead of the DMV.
In the scene in the library before the ghosts appear, it starts to get really cold. Shaggy breathes and you can see his breath. However, when the others in the room speak, you can't see theirs.
When the teens are serving their detention in the library and the weather storm begins, at one point Velma says "unusual 'climactic' anomaly" referring to the impending weather storm. In fact Velma should have said "unusual 'climatic' anomaly. Her use of the adjective is in error as "climactic" refers to the word "climax" whereas "climatic" would be the adjective to use when referring to "climate."
In the scene where Shaggy is having trouble driving the van out of Daphne's garage and reveals that he just got his license, Velma grabs his right hand and tells him to put it at 10 (10 o'clock position on the steering wheel) and his left hand at 2, but it should be the other way.