Trivia: When Rory is walking down the street wearing the Predator mask, there is a bright red/orange alien walking toward him. This is a nod to the original Predator costume that looked like a big bug, the red/orange color was used to film the stealth camouflage scenes. The bug suit was scrapped after a few test shots proved how silly it looked. Jean-Claude Van Damme was in the original costume, but he was let go when the costume was scrapped. (00:45:20)
Trivia: Spoilers. Originally, Shane Black wanted Arnold Schwarzenegger to make a cameo in the end - he would have been the "Predator Killer" that rises from the device right before the credits. When he decided not to return, the "Predator Killer" was changed into a highly advanced suit of armor.