Human beings alone are the most complex and disturbing species in the universe. But when inhabited by a mind-controlling, parasitic creature, they’re far more unpredictable and dangerous. So what is it that really creeps us out about these fictional barnacles? Its take of unnoticeable shape-shifting forms? How about the zombie-like presence they place victims under? Or is it the repulsive tendency some have of shooting a slug-like creature into your mouth? Answer: All of the above. So as we search for some great horror films heading into Halloween, we revisit the classics that got under our skin in more ways than one. Here’s a look at the 9 Scariest Parasite Films of All Time. Trust no one.