HEADCRABS – Half-Life series
Headcrabs are small parasitic monsters that resemble an uncooked chicken with four slender crab legs. Their mouths are found underneath their body, sharp beaks that allow an almost impossible-to-break grip once the headcrab attaches itself to a host.
Headcrabs are very fragile, dying quickly to bullet shots or a good smack with a crowbar. Their inability to withstand blows is made up by their ability to pounce great distances, often emitting a guttural squelch before pouncing for an attack. Their main advantage being their large jumping range, headcrabs will usually try to ambush their prey, leaping out from air-vents or from behind crates.
Once on a victim, the beak-mouth works like a can-opener and the headcrab attaches itself to the skull of their acquired host. The toxins in the headcrab’s bite corrupt humans, and are mutated into a zombie-like creature that tries to kill anything it can, presumably allowing the headcrab to change hosts if need be. The human host undergoes a number of hideous transformations depending on what species of headcrab infects them.