Factual error: The Air America helicopter that flew Tom Hanks and company out to the site was a Bell 212 (Twin Huey) The movie allegedly takes place in 1962. That model Huey was not introduced until 1968.
Continuity mistake: When Monty punches that guy at the end, check out how the parting of his hair goes from left to right and back again in one shot as he falls and gets up.
Continuity mistake: When Charlie goes to jail he sits on the bed and bums a cigarette. Then the next morning he is lying on the bed and bums another cigarette. His bed changes heights in each shot. (01:30:50 - 01:31:25)
Continuity mistake: When the lads run over the fire hydrant in Jonathan's father's Studie, the bumper appears undamaged. However, when they pull up in front of his house, the right side of the bumper is badly crumpled.
Factual error: There is a scene in which the Catholic high school boys are lined up to go to Confession to a priest. One of the minor characters is a compulsive masturbator, a recurring gag in the film. He is trying to estimate how many times he has wanked since his last Confession, and Kevin Dillon's character takes out a digital calculator to help him figure it out. The film is set in 1965, about 8 years before personal calculators hit the market. (I was precisely the age of the characters in 1965, and we would have sold our souls to the devil for such a device. It was still science fiction!).
Continuity mistake: The judge arrives and tells the audience that they can sit down. The guy on the left with a white linen shirt sits and crosses his left leg. Reverse shot, and he is repeating the action, this time crossing his right. (00:03:20)
Visible crew/equipment: During the final battle, when the Ewoks swing on the ropes, a crew member's hand is visible pushing one of them forward.
Continuity mistake: When John Candy is woken up by his wife after getting drunk with Scully, he has a hoop earring in his right ear. Later during the regatta, the earring appears in his left.
Continuity mistake: Everyone wears the same outfit during their hunt for Big Bird. Maria's changes to a dress once they arrive in Toadstool.
Visible crew/equipment: Near the beginning, at the start of the big car chase down the hill, there is a guy blocking another guy's vehicle. The blocking car is red and backs up before turning onto another road. The reflection of the entire camera crew is visible in the side of the red car.
Audio problem: When the husband (Hector Elizondo) is seated in the barber chair, he's heard talking to the kid, but his lips aren't moving. An obvious audio sync issue.
Other mistake: When Dagg hits the soldier on the left while the fembot is distracting them, he falls over and the one on the left turns to see what happened. It then cuts to a different view and suddenly the second soldier just falls over without even getting hit.
Continuity mistake: During the scene when Andrea's talking about suing the club, the amount of papers in her hands change from 4 to 5 in between shots. (00:44:20 - 00:45:21)
Continuity mistake: The old lady grabs a knife and throws it at Jack Deth. In the wide angle he lets go of the stove, but in the next shot he's still clinging to it with his left hand. (00:05:05)
Continuity mistake: When Dalton is having his picture taken with his camera by the blonde next to the pool, she has his camera. Christopher confronts him, then in the next shot Dalton now has the camera and the blonde is holding red roses.
Character mistake: Morgan Hiller's father is named Stewart (according to the story as well as credits). But in one scene when Morgan and his parents are having dinner, Mrs. Hiller calls him (her husband) "David" one time (instead of Stewart).
Audio problem: When Quatermain and Jesse are fleeing in a stolen truck, they are being chased by people in other vehicles. Even though all the streets are dirt, there are numerous times when the tires of all the vehicles squeal.
Character mistake: When David Frost interviews the fictional actor Bryan Martin, he adds a last question to the interview saying "before you go" and acts as if the guest is not gonna stay (as it often happens in talk shows, when some guests, especially the more famous ones, leave after their bit is over). However Martin is staying and in fact there is a special mystery guest a bit later that makes sense only if he is in fact staying. (00:02:00)
Audio problem: During the live performance of Kurtis Blow, on the hook, the girls singing backup have the mics in front of their mouths. His vocals would have faded away when they moved the mic. (00:33:18)
Continuity mistake: When Gun is having lunch with the Sensei, Gun picks up a bowl of noodles as well as two chopsticks. At first, the two chopsticks are facing outwards. But in the next shot, the two chopsticks are facing inwards toward the bowl. (00:03:53)