Audio problem: At his "pool party", Mr. Saint is talking to a group of men, and there is a female singer standing in the background, her mouth is moving as though she is singing, but there is only music from the band.
Continuity mistake: After Frank shoots Howard Saint, when he goes to tie him onto the car Howard's hands change from resting close to his belly to resting on the floor.
Continuity mistake: When Frank is positioning the fire hydrant he has trouble moving it due to its weight. Yet only a minute earlier he was carrying it quite easily in a bag a good few inches above the ground.
Deliberate mistake: When Saint is being dragged through the parking lot with all the exploding cars, there are a few shots where it is obviously just a dummy instead of John Travolta (the actor who played Saint).
Visible crew/equipment: When the bad-guys blow Frank up towards the beginning, as they drive away the camera pans with the car, and you can make out the shadow of several crew members and possibly the camera at the bottom right of the screen.
Factual error: When the Russian tears the toilet up to throw it at Frank, the room should be awash.
Continuity mistake: Towards the end of the film, Castle is setting up his revenge wearing a trench coat but when he is placing the fire hydrant, it is the same footage from earlier when he had a T-shirt on.
Continuity mistake: When Howard is killed, he's set on fire by all the explosions. Yet just a few seconds later in a wideshot, he's no longer on fire.
Revealing mistake: When the car Howard Saint is tied to explodes, watch Howard's body - it's clear that he's been replaced with a hilariously obvious dummy. It's especially comical if you look at his legs, because it appears that the dummy doesn't even have legs inside of its pants given how they "wobble."
Revealing mistake: When Frank kills Howard Saint at the end of the film, pay close attention when the cars start to explode. About a second-and-a-half after the first explosion, the camera cuts to a high-angle shot looking down at the cars exploding. Pay attention and you can see a lot of errors. For example, there are two cars (one red and one blue) on the right side of the screen that are teeny-tiny models and aren't properly blended into the background with blurry edges around them. Additionally, the three cars on the bottom left of the screen also have noticeable black lines around them. (Likely from a poor compositing job.) It appears the shot was created with different miniatures layered over a background plate, and the various miniatures weren't properly comped into the shot.
Continuity mistake: Castle ties Saint's left leg to the car bumper. A few seconds later it's suddenly his right.
Character mistake: When Howard's men bail the guy out who was with Bobby Saint at the arms deal, they are beating him up in Saint's club. Howard Saint (John Travolta) shoots the man responsible for not watching his son. The man fall down to his knees and then says the name John instead of Howard.
Continuity mistake: Toward the end if the movie when Castle goes to Saint's compound to exact his final revenge, the first guard he kills is with a bow and arrow. Castle shoots him in the back but when the guard falls forward he reveals Castle on a perch directly in front facing him.
Continuity mistake: At the end when Frank ties Howard's leg to the car, Howard's arms are on his stomach, then extended out, then on his stomach, then out again.
Continuity mistake: On the pier, where Frank's wife and son are killed, his wife is in the background lying flat on her back, dead. Later in the same sequence, she is suddenly lying on her side.
Character mistake: The newspaper states Frank's son as being 10 years old. But according to the headstone dates, he died at age 8.
Continuity mistake: When Frank is at Saint's building, he starts throwing money out the window. Problem is, its showering down in single bills and it is originally wrapped in bundles. The cart is stacked to the top and it would take time to unwrap all the bundles.
Continuity mistake: When Quentin pulls out Dave's eyebrow ring, there's no ring in the pliers.
Revealing mistake: After The Russian smashes The Punisher's refrigerator door against his head a couple times, he shoves The Punisher to the floor and pushes the refrigerator door shut, but the refrigerator door suddenly and completely stops moving midway before closing, revealing the door to have a stopper built in so as to not actually hit the actor in the head with it (acknowledged by the director in the film's commentary track).
Continuity mistake: When Frank reveals himself to the public in front of a group of reporters and two former co-workers - when we first see him, you can see he is wearing a black button-up shirt that is buttoned all the way up, except for the top two, revealing that he is wearing his skull t-shirt underneath. (You can see the top of the skull peaking out.) But a few shots later, the bottom half of the shirt is completely unbuttoned (only one button is actually buttoned up), with him having no time or reason to do so between shots. In addition, when the bottom half half of the shirt is unbuttoned, you should be able to see the rest of the skull, but you can't. You can tell the skull just sort of stops midway down the shirt, revealing that he is wearing an alternate version of the t-shirt that only had the top half printed on it, so it would be just visible peeking out of the top of the button-up shirt.
