Continuity mistake: When Harold and Kumar stop to take a pee and then leave, Harold gets bitten by a raccoon. In one shot Harold's blood stain is seen on his jacket, but in the next shot it's gone, then back again and so forth, until the car comes to a stop.
Factual error: When they stop at the gas station to ask for directions, you can see a Country Style donuts sign on the outside wall. Country Style is a Canadian brand.
Continuity mistake: In the scene with the diarrhea twins, when Harold and Kumar go into the middle stall, you can see that all of the doors are closed. When the twins are standing at the mirror in the bathroom, you can see that the door, in the mirror, behind the twin in pink is open.
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.
Continuity mistake: When Kumar is at his interview for med school, the dean of admissions spills his coffee on himself and puts the coffee cup back on the table, but between shots the handle of the cup changes directions.
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.
Factual error: Near the end of the movie where H&K are stealing the skateboarder's truck, there is a Shoppers Drug Mart in the background. Shoppers Drug Mart stores are only located in Canada, not New Jersey.
Revealing mistake: When Kumar is clipping his pubes in Harold's mirror, when they go to a close up of Kumar's face and torso when he's speaking, you can see the blue shorts he's wearing for the shot. When Harold entered the room we can see Kumar from behind nude facing the mirror.
Continuity mistake: Harold's Toyota Camry changes between shots a few different times in the movie. In the beginning and for the majority of the movie, the Camry is one of the more expensive trim levels with alloy rims. During some of the shots, it switches back and forth from this to a base model Camry with wheel covers. One of the times this happens is when they are wrestling with the raccoon.
Continuity mistake: When Kumar is interviewing at Princeton, the cup is not only changing directions, but sometimes is missing and at one point it is sitting slanted on top of a pen.
Continuity mistake: When Harold is given the paperwork to do by his boss in the beginning of the movie, his boss is giving him an "okay" sign and a "number one" sign with his right hand. The last shot before his boss leaves, he put down his left hand, which he was not using to make the signals.
Continuity mistake: As we see Harold and Kumar in the car we see a close up shot of Harold on his laptop. We also see a USB wire in the side USB port to which is attached a small light set off to the left of the screen. In one of the wide shots this light can be seen, but in all the others it has disappeared.
Continuity mistake: When Harold and Kumar almost get in a car accident, Kumar rolls down his window all the way down when talking to Goldstein, but the next shot of Kumar opening the driver side door, the window is now only half down instead of all the way.