Propeller Trap

This is one of the three main traps used in the Half-Life 2 level "We don't go to Ravenholm..." by Gordon to fend off the many hordes of Headcrab Zombies. It kills any enemy instantly and deals massive damage to Gordon if he walks through it. It is activated by ducking under the blade and pulling a lever. Once the blades are spinning, the only way to get around it without any damage. is to duck and crawl under it. It is made of a car engine turned on its side with a metal pole sticking out of it connected to a very sharp piece of sheet metal on one end, and a counter-weight on the other.