Deliberate mistake: Towards the end of the movie, when Van Damme and the Sandman are fighting in the boiler room, the Sandman gets kicked into an open furnace for some time and then jumps out covered in flames. It's noticeable that he still has a full head of hair, which is impossible. Hair would be the first thing burnt right down to the scalp within a matter of seconds.
Deliberate mistake: It's not particularly believable that the away team to stop the assassination would consist of the ship's entire senior staff, and raises the question of who was left in charge of the bridge (the answer: apparently nobody, as they return to a completely deserted bridge). Of course this is dramatic license, and at this point the audience won't care or likely even notice.
Deliberate mistake: The "flow" from Fred (Rachel's brother) urinating while strapped to a chair was not what would be expected. His pants would absorb the urine, so urine would not flow to the floor like from a faucet or large streams drip straight down and form a puddle beneath him. (00:57:06)
Deliberate mistake: There's a bizarre editing gaff in the opening fight of the Director's Cut. At one point, Fasil's sword vanishes (for no real reason) and he starts to do backflips. The scene then cuts away, and when it cuts back, he's suddenly running and has his sword again. A few shots later, he's suddenly doing backflips and has lost his sword again. (It's meant to be Fasil doing the flips.) The editing makes absolutely no sense. It's like they somehow mixed up two different scenes during editing.
Deliberate mistake: In the last sprint towards the finish line, before they have to race on foot, the Lamborghini passes Fenderbaum and Blake. The red Ferrari they are supposed to be driving, is on the bed of a truck being towed. Notice the height difference between the two cars; about ten seconds later the two cars are pretty similar in height. (01:23:05)
Deliberate mistake: In the Director's Cut (the version most readily available on DVD), there is literally an entire 15-second chunk of the final fight that is repeated twice within 60 seconds. (It's the bit where Duncan and Kell are fighting on the ground, Duncan kicks Kell, then Kell kicks and slices Duncan) It's impossible not to notice, and it's not they're flashing back to what just happened... they just repeat the same 15 seconds of footage, add different sound effects, and assume people won't notice.
Deliberate mistake: When Hellboy is attacked by the spider-lady, as the spiders begin to descend on him to steal the sword, you can easily tell that some of the shots of the spiders coming down are repeated 2 or even 3 times, and simply flopped horizontally to appear different.
Deliberate mistake: When Steven Seagal and Kelly LeBrock are in the jeep, being chased through some fields by the cops, some of the shots of the jeep are flipped. Note the bullet holes on the windshield switch sides, as does the driver/steering wheel, the windshield wipers and the front license plate. As an aside, also note the numbers/letters on the license plate that have been altered via CG in the flipped shots.
Deliberate mistake: The entire plot wouldn't exist without this one, but just before the engineer stumbles out the door and falls off, he pulls the big red lever on the left side of the cab. In the real world this puts the air brake system into its emergency mode. Among other things, this mode trips a solenoid which causes the engine to return to idle, and the electrical system to not put out power. Neither the Diesel engine nor the electrical system will respond to control inputs until/unless the air system is reset.
Deliberate mistake: When the platform Jackie and Rathbone are on falls, you can see a shot of a restraint snapping out of the floor. Two cuts later is the same shot, just flipped horizontally.
Deliberate mistake: When Connors becomes a humongous Lizard, his robe magically grows from a Medium size to an XXL. (01:06:50 - 01:17:45)
Deliberate mistake: Although the first account of what happened in Zhao isn't completely true, the arrows penetrating the calligraphy school are sometimes flying at angles that make their trajectory impossible, such as arrows flying perpendicular to the ground or even flying upward.
Deliberate mistake: When Jackie tries to avoid the Jamaican guy he jumps up to a higher deck. As we see him duck out of sight it takes him about 1 second to get to the other side and jump down there. However it's at least 40 feet to get to the other side. Jackie is usually fast but not that fast. (00:34:30)
Deliberate mistake: At the end, when the applause sign falls on Rocco's mom, it should stop working. (01:10:35)
Deliberate mistake: The nose pieces on the face masks have been removed from all of the SCBAs used in the movie. The nose pieces are essential to keep the mask from fogging up, but were removed to allow the audience to see all of the actors' faces.
Deliberate mistake: During the scene where Ryback is fighting Penn (the grey-haired mercenary) in the kitchen, watch for the shot where Ryback flips Penn. The film has been sped up and the result looks disjointed and out of place. The characters are moving FAR too fast for it to look natural.
Deliberate mistake: During Dade's first 'hacking' scene, he is wearing sunglasses. The shades disappear for a closeup shot of Dade's eyes and a brief montage of TV clips, then reappear on Dade's face in the longer shot. (00:05:45)
Deliberate mistake: Ash's car breaks out into the courtyard and the whirling, windmill thing batters the Deadites aside. We see the carnage a couple of times filmed from different angles, one Deadite, planted, legs apart, gets battered twice and the guys who come in from the left and are quickly jerked off screen are shown again seconds later.
Deliberate mistake: The pile of fish in the first fish trap is much taller than the trucks. That's impossible without some sort of lifting equipment - and no such thing is around in the aerial shots. (00:42:50)
Deliberate mistake: After Doug finds where Minuti was killed and set on fire, he walks over to a dock where he sees Minuti's arm being eaten by alligators. Minuti had been dumped in the water 4 days prior, yet his hand is perfectly intact with no signs of burning, bite marks or weather/water damage of any kind.