John punched the snake.
The snake, confused, as he had never been punched before, hesitated for a second, then bit John in the ankle. The ankle tasted yucky. Dust, sweat and bug spray. The snake recoiled in disgust.
John watched the snake slither away, then examined his ankle. Four little punctures in his skin. He knew it was all over. He could feel the poison creeping into his system. It was a three day walk to civilization. He sat down to die.
Two days later the rangers found him hungry and dehydrated but otherwise healthy. Snakes are not all poisonous.