Trouble is
Adders sometimes play dead when they are faced with insurmountable danger - hence playing dead in front of a car and becoming just that!
We found a baby one last year. We were out walking (sadly didn't have my camera), and a car came along a quiet country lane. After it passed my son pointed and actually went to pick it up, but luckily I stopped him in time - not sure at what stage they become venomous! It was only about 2 inches long and was so still we were almost convinced he was dead. Just in case, I found a twig and managed to hook him up and put him in the hedge out of harms way. We marked the spot for our return, and when we checked he was gone, so obviously was still alive!