The undead have an insatiable appetite, devouring everyone they can reach. Usually they will eat a small portion of a victim and then lose interest as the meat turns cold and starts to reanimate into another undead.
Sometimes however, they enter into a feeding frenzy, stuffing themselves with as much of a body as they can fit inside their stomach, often causing their internal organs to burst and leak whatever they are eating back to the ground.
Common and ravager undead can often be seen in a feeding frenzy. They will ignore other living people around them, unless shot at or provoked, then they will stand up and come after you. Running over a feeder will grind lots of gore into your wheels, temporarily slowing you down quite a lot.