Deliberate mistake: When Lex tests the crystal fragment, it knocks out all the power on the airplane Lois is flying in, yet the flight attendant's amplified voice can still be heard over the speakers. (00:30:40)
Deliberate mistake: When Zoom is moving the documents from the desk to the floor for Marsha to pick up, she quite blatantly catches him two or three times, but continues on with her business.
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: 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.
Deliberate mistake: Throughout the movie, Seagal's voice changes. In some scenes, his lines are spoken by someone else (with a much coarser voice) and dubbed in, which is confirmed by numerous sources over the internet.
Deliberate mistake: When Jenny writes "dick" on Matt's forehead, she does not stop the beam but the word is written with the letters separated.