Continuity: When Harold and Kumar are hiding in the girls bathroom and peeking out over the top of the stall, the feet of one of the sisters can be seen in the stall next to theirs before she is actually shown going in.
Continuity: When the extreme punks are in the store, and NPH steals Harold's car. Harold and Kumar look around the parking lot, the extreme Ford truck is missing, even though the punks are still in the store.
Continuity: When Kumar was on his cell at the start of the movie and he shocks the principal, the guy drops his cup of coffee and it spills on him. However, in the next scene, it appears back on his table. After Kumar is done and when the guy starts to talk, we can see that the cup is nowhere to be seen on his desk.
Continuity: In the beginning when Billy says he owes Harold "just one", he initially points with his left hand, but subsequent shots show him using his right.
Continuity: Harold's car (2003 Toyota Camry) has alloy wheels, yet when they pull over for Kumar to urinate in the woods, the car has cheaper hubcaps. When the raccoon climbs in you see a close-up of the alloy wheels again, then again see hubcaps as the car pulls away. Not only that but Harold's car has leather seats, throughout the film yet at the shot of the drive through at burger barn, you can see that the car has cloth seats.
Continuity: When the Burger Shack guys goes insane and yells, "Let's burn this mother down," he loses his hat while knocking things down. But when he rises to talk to Harold and Kumar, his hat is back on his head.
Continuity: When Harold starts yelling about having no money at White Castle, he bangs down on the counter knocking over the yellow mustard container. The mustard is alternately standing/lying down in subsequent shots.
Continuity: The fog lights on Harold's car repeatedly alternate between on and off over the course of the entire movie.
Continuity: When Kumar stops the car and urinates on the bush, the street sign changes direction repeatedly between shots.
Continuity: When Harold and Kumar escape from the cops in Princeton, Kim, the twins and the "I'm so high kid" are in a corridor that is well lit. When the camera moves over to the other side, that corridor is empty and dark.
Continuity: When Harold and Kumar are looking through the window of the Hot Dog heaven, a cup on the table says "Licks". Licks is a burger chain where the movie was filmed.
Continuity: In the beginning of the movie, when Kumar is meeting with the interviewer for the medical school, the mug on the desk continuously disappears and reappears between shots.
Continuity: The cut Harold receives from the extreme punks grows as the movie progresses.
Continuity: In Kumar's Med school interview, his collar alternates position. He begins tucked with tabs in, then one side tucked under his jacket, then both tabs out, then the opposite tab tucked, completely tucked in, then both out.
Continuity: Before the raccoon climbs into Harold's car, he picks up his laptop to do some work, and his glasses are off. When we cut back to his face, he is wearing his glasses.
Continuity: When Harold and Kumar board the hang glider, it is early morning. However, subsequent shots to the police car that is (still) chasing them show the car driving through the forest at night.
Revealing mistakes: The wire that is holding the hang glider is visible in several shots, especially when Harold and Kumar hit the tree.
Continuity: When the two girls are in the bathroom putting on make-up, if you look in the mirror, the door of the stall, to the left, is open in one shot and closed in another.
Continuity: When Harold and Kumar almost run off the cliff in the punks' SUV, the front left wheel is hanging off the cliff in mid-air. A few seconds later, as they hear the siren and Harold says, "We're trapped!" the wheel is on solid ground.
Errors in geography: At the gas station, a "Country Style" donuts sign is visible on the outside. This is a Canadian chain of donut stores which would not be in New York/New Jersey. Other Canadian stores such as Shoppers Drug Mart and Chapters (a bookstore) can also be seen.
Crew or equipment visible: When Kumar stops the car to urinate in the bushes. As raccoon climbs in the back seat of car, the puppeteers hand and the puppet stick is clearly visible between the front seats.
Revealing mistakes: Throughout the movie you can clearly see Harold's laptop bag fold in the middle showing there is no laptop in the bag. Particularly visible at the gas station.
Continuity: After Kumar falls from the air conditioning duct above the police station he bumps his head on a filing cabinet. In previous shots, however the filing cabinet was nowhere near the spot where he fell.
Continuity: When Harold and Kumar are about to eat the burgers, Kumar stops Harold from eating his burger so they can bite into them simultaneously. Prior to this, Harold's burger is still in a box and suddenly it's out of the box.
Continuity: Freakshow's wife opens her shirt twice.
Continuity: When the cops run into the business hippie at Princeton the big bag of pot flies out of the backpack but when they pick up the hippies backpack the pot is back inside.
Continuity: When Harold arrives outside his apartment building after eating at White Castle, his car is covered in mud splats, etc, supposedly from when NPH took it on the joy ride. But when Harold and Kumar come out of White Castle and get into the just a few moments earlier, it is spotless.
Factual errors: The cheetah can be clearly heard roaring during the film. Cheetahs cannot roar, they can only purr, hiss, and growl.
Factual errors: When Harold and Kumar are arguing outside the gas station, a sign that says "Self Server" can be seen in the background of the shot by the pumps. New Jersey does not allow self service at gas stations, only full service.
Continuity: When Harold and Kumar almost crash into Goldstein and Rosenberg, when the two approach the car, Kumar rolls the window down all the way. Then in the next shot where you see Kumar get out of the car the window is slightly up.
Plot holes: While the geography of New Jersey in the movie is very accurate during Harold and Kumar's journey from north Jersey to south Jersey, there is simply no need for them to have driven so far to find a White Castle. The trip from Hoboken to Cherry Hill is 85 miles and takes about 2 hours (without traffic), and there about 20 White Castles along the way. In fact, Harold and Kumar didn't even have to get on a highway to find one; there is a White Castle on Kennedy Boulevard in Jersey City, which is adjacent to Hoboken.
Revealing mistakes: When Harold almost drives the Extreme 4x4 off the cliff, a metal structure can be seen holding the car up. Later in the wide shot when the police arrive, the same metal support can be seen.
Continuity: Harold and Kumar reach Burger Shack thinking that there is a White Castle there. They leave after the employee tells them about the "secret sauce." As they are driving away Kumar says "Remember when Goldstein worked there?", yet moments before they had no idea that Burger Shack was there.
Continuity: The blood stain on Harold's shirt disappears for a few shots. After the raccoon scene when they almost collide with the car on the road.
Incorrectly regarded as goofs: The slider special (as shown on the TV commercial at the beginning) is $2.99 for 6 burgers, fries and a drink. If they ordered 5 specials each, their bill should be just under $30 before tax, and yet they are charged almost $50. However, in the finale they order separate items (30 burgers, 5 fries, and 4 drinks each). Unless the server converted that order into specials (8 specials, plus 10 burgers and 2 fries), they would not get the cheaper price.
Continuity: The rear-view mirror is present in some scenes and missing in others where we see Harold and Kumar though the windshield of their car.