I'm trying to figure out the name of a movie I saw on TV when I was a kid (late 70's?) Not sure if it was a TV movie or a theater movie played late on a Saturday night. Some people visiting a friend on an island are being stalked by a supernatural monster made out of mud. At one point they fight the monster at the door of the cabin it has trapped them in and they cut it's hand off on the door. The hand runs around on it's own and later trips somebody on the stairs in the celler. I remember something about throwing salt on it to kill it. It ended with them managing to lure it onto the boat dock and dumping it in the ocean. Any title suggestions would be appreciated.