Cannibal Ferox (1981)

Cannibal Ferox (aka Make Them Die Slowly) (1981) is an Italian exploitation/horror film starring Giovanni Lombardo Radice, Bryan Redford and Danilo Mattei. It begins with a college student and her group of American friends out to confirm the girl's college thesis that cannibalism isn't real by venturing in a forest in South America. The intrepid anthropologists become lost and run into jungle savages imprisoned by drug dealers. When they escape, they commit brutal acts of sadistic torture, brutality and unspeakable cannibalism against everyone in their path. The violent film also features scenes where real animals were actually murdered.    

One very gory scene includes Radice's character being is tied to a tree with his penis and balls exposed before prosethetic verisons are hacked off and eaten by the cannibals.