80's Horror Movie?

There was a movie in the 80's that was about monsters, or mutants in the jungle. I don't remember the full plot, but the ending was that the helicopter came to save the last survivors, and as they were flying away. They thought they were safe, but a monster popped out of the back of the helicopter, from behind a curtain.

This ending was even spoofed on an episode of the Simpsons about Tomacco, when Homer had a farm and genetically spliced tomatoes and tobacco, and the animals went nuts, at at the end a sheep popped out of the back of the helicopter as the execs were trying to escape.