Tremor

Overview

These are leech-like creatures, come in various sizes and two colors: blue and red, with the red ones being slightly more damaging than the first. They slowly crawl along filthy floors, walls and roofs, and will usually make no effort whatsoever to attack Henry. However, if the player walks on one or one falls from the ceiling onto him, he will take damage. Henry will take no damage if he intentionally stomps on one, though, so that's usually the way to go with the Silent Hill 4 monsters.
On the Water Prison, Andrew DeSalvo forcer the young Walter Sullivan to drink water with leeches in it.