Continuity: As Harold and Kumar drive Neil Patrick Harris' car through Alabama, the license plates on the car clearly read "Virginia", but for one scene as they enter Texas, the license plates read "Texas". Then, later they are back to "Virginia".
Continuity: When Harold and Kumar are smoking with the president, he (the president) puts down his joint while talking about what it means to be an American, but then is seen holding it the next time he is cut to. This continues two or three more times in the scene.
Continuity: When Harold backs the yellow sports car into the fire hydrant, the hydrant topples over and water gushes everywhere. But in a closeup of the rear of the car a short time later, there is no damage to the car, not even a scratch on the bumper.
Continuity: When escaping from the Fox Hole whore house, the window on the car Harold is driving is shot out. In the next scene, the window is intact.
Continuity: The passenger side head rest disappears and reappears between shots in the Chevy Cobalt Neil Patrick Harris is driving.
Revealing mistakes: In the shower scene when Kumar is on the toilet you can see the outline of his under pants when he turns.
Continuity: The bandage across Harold's eye moves or disappears throughout the beginning of the movie.
Factual errors: The device Kumar finds in the car, and uses to call Goldstein, is a Nokia 770 Internet Tablet. It is not even a phone, and is wrongly referred to as Nokia 7710.
Revealing mistakes: Neil Patrick Harris's car has cloth seats, but when Harold and Kumar are shown hiding under the blanket during the check point entering Texas, the seat appears to be upholstered in leather.