This slug like parasite is actually a symbiote. After attaching itself to a warmblooded host, it feeds off that being. However, its tenticles, growing under the skin, act as secondary nerves, increase the victims nerve responses.
A certain culture believes that evil can live beyond the grave. They also believe that the destruction of the dead body can keep that one from coming back. Destroying the newly deceased body can destroy the soul if done properly. They first burn the body for 24 hours, smash the remains as well as possible, then burn the what is left for another 24 hours.