Other mistake: In the slaughterhouse scene, after Harrigan has injured the Predator with his shotgun and Keyes reappears, the Predator throws its disc, and severs Keyes in half at the waist. We see his legs flop to the ground, and blood pour from above, but his upper half (torso, backpack and weaponry) mysteriously remain hovering out of sight. (01:21:50)
Other mistake: When Carl has received the Nassau bank account number from the drug dealer on the phone, afterward you see him typing in "Rita Miller" on the computer. If you watch closely, his left hand pinky never touches the "A" key on the keyboard, yet the "A" in Rita comes up just fine and out of sync with the clicking sounds of the keyboard.
Other mistake: The close up of the Wall Street Journal mentioning Immobiliare seems to have operating instructions for a Windows program under the headline. The newspapers previous to this appearance also have a headline pasted onto another news topic altogether. The same happens later with the newspapers covering cleansing actions of the new pope. These papers date from March 27, 1980, although the events are supposed to take place in 1979. (00:41:42 - 02:00:00)
Other mistake: When Harrison Ford returns to the crime scene to search for "evidence" we see blood stains on the carpet, which has been on the carpet for days. The blood is bright red and shows no signs of coagulation, but blood turns dark red when it coagulates after only a few hours.Frank Scialdone
Other mistake: Irv and Blaire's death scene doesn't make sense. When Irv poured butter on the popcorn, he should've noticed the spider in the bowl. Also, when Blaire picked the spider up, she should've felt it. Both of them still appeared to be watching the TV after being bitten, which also didn't make sense. Why didn't they have seizures like the other victims?
Other mistake: After Arnold kills Harry and his gang at the beginning, how did that blood splatter get on the wall behind him to his right? He shot the henchman standing in that position from the back and the other who was shot was shot standing to the left side of the wall. So there is no explanation why the splatter is there.