The Blood on Satan's Claw (1971)

When a mysterious corpse is accidentally dug up by a boy in a small town, a group of local teens starts acting very strangely. The adolescents, led by a girl named Angel (Linda Hayden), are convinced the corpse was once possessed. Hoping to get in touch with the devil through the body, the teens act out a series of demonic rituals that causes a stir among the townspeople. When word of the satanic activity spreads, certain parents start trying to lock up the kids behind the spooky stunts.

The second in the triumvirate of films that would help define the genre. The other two are: Witchfinder General (1968) and The Wicker Man (1973).