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: About one hour in, Maerose is sitting at the table talking to her father. Every shot from the front shows her with her right arm across her body, but every shot from the rear shows her arm forward on the table.
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: Everyone wears the same outfit during their hunt for Big Bird. Maria's changes to a dress once they arrive in Toadstool.
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: 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.
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.
Revealing mistake: When he old lady jumps over the counter to attack Jack with a cleaver, she is replaced for the physical struggle by a younger person; you can see her face when the two struggle against the table. (00:04:55)
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.
Visible crew/equipment: At the end when the helicopter is hovering above the two guys fighting, we see the shadow of the camera on them multiple times.
Other mistake: Most of the obvious misses and awkward parts of the action in the opening can be attributed to the fact that it is revealed a few minutes later being just a drill. However, it does not make sense on any level. The training makes use of live explosives, and at the same time no gunshots are fired but only grenades, with unrealistic trajectories and range. The 'terrorists' don't use their rifles if not to try and bash the good guys on their skulls. That's quite the subpar training, but the top brass are impressed.
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).
Continuity mistake: When the men posing as painters rip off the drug dealers, they place a scaffolding plank to cross to the other building, which they remove from the windows and it falls onto the street. When Chuck Norris enters the apartment it reappears.
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)
Revealing mistake: During the opening assault, notice that the sandbags of the enemy fortifications are more like fluffy pillows; they are squashed under a single person leaning on the bank, and they wobble and nearly fall over when Carrasco himself brushes the hip against them walking by. (00:04:30)
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)