Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a jungle adventure movie based on a book which is based on the true story of Percy Fawcett, an English Army officer who was sent to South America to make a border survey. In the jungle he finds some old pottery and becomes obsessed with finding what he is sure was an ancient lost city in the Amazon. He becomes a world-wide celebrity explorer, but he disappeared without proving that the ancient city existed. Maybe he was ahead of his time - over one hundred years later, signs of ancient civilizations in the Amazon have been found and are still being investigated.
The snake scene is very brief:
Fawcett and his assistant Henry are in the middle of the jungle surveying the border between Brazil and Bolivia in 1906 when Fawcett sees a juvenile Boa Constrictor crawling at his feet. He thinks it's a deadly snake. It isn't, but it is species they could have seen so I commend the film for that. If they were American explorers they would have blown the snake into a million pieces with their handguns, but these are English explorers who always keep a stiff upper lip, so Fawcett simply lets the snake crawl right through his legs without interrupting his work.