There are few more surefire ways to know a person is certifiably insane, then having him keep a completely inanimate rotting corpse around to keep him company. This is most often occurring when a loved one passes away before the one they leave behind is not ready for them to go, so the one left behind decides to keep the body around as if it were still alive. Sub trope to "Talking to the Dead" because there is a major difference between talking to a grave, and plopping that corpse on the couch to have a face to face conversation. The Walking Dead video game inspired this for me, but I felt like I've seen this this has been used in many stories before. I just can't put my finger on them. Doesn't Friday the 13th play with this?
Hello, Unknown Troper. You'll need to get known to lend a hand here.