Three friends out to disprove cannibalism meet two men on the run who tortured and enslaved a cannibal tribe to find emeralds, and now the tribe is out for revenge.
Details would be just as triggering to read for some people, so I won't do that... but this film (and the entire mondo/cannibal genre it occupies) is well-known for its relentless gore and graphic realism/intensity. Lots of it.