Talk about fearless ... contestants on "Naked and Afraid" saw how a snake nearly killed one of the TV show's producers -- and still refused to back out of the competition.
Sources connected to the Discovery show tell TMZ the players were warned after Steve Rankin was bitten by a poisonous fer-de-lance snake while location scouting in Costa Rica. Rankin barely survived, and as we previously reported ... the flesh rotted right off his foot.
We're told honchos warned players they could face the same fate as Rankin, and gave them the option to quit the show ... which drops naked contestants into the wild and watches them survive.
No one backed down from the potentially deadly danger.
Warning: You can see that danger HERE (if you dare).
The first episode airs tonight, and if you've ever wondered how you'd start a fire if you were butt nekkid in Africa -- watch this clip.