Revealing mistake: In shots of the drive-through guy at the the Burger Shack, it can be seen that the restaurant has no back wall.
Revealing mistake: After they almost drive the Xtreme truck off of the cliff, Kumar gives a speech on their ancestors. He appears to be standing too far in front of the vehicle, which is partially over the cliff. In some shots in the same scene we see him standing on a short outcropping, but the angle of him to the vehicle doesn't match with the earlier shots.
Revealing mistake: As Harold and Kumar are driving through Newark they observe some guys beating up a 'lamer version of them'. Right after Harold and Kumar say "Holy Shit" we see the gang stop, pause and then start again. Watch the guy in the green beenie hat as he swings the baseball bat. He makes to hit the guy on the floor but actually stops the swing about three feet above him.