70's or 80's Jungle Ghost-Killer

by David Dix

Does anyone remember this late 70's or early 80's supernatural horror film set in the jungle where a man walks into a small cabin and sees a snake crawling through the eyesockets of a human skull?

In another scene, a couple is going at it on the ground and a knife comes down on top of them, killing them both (ghost?)

In another scene, a man in camouflage or green clothing is sitting in a tree with a gun. The killer has cut his throat.

Any ideas?