I heard a true one years ago on NPR. As I remember it:

A fellow was riding along on a mule, going down into the Grand Canyon on a tour being led by a park ranger. At one point his mule got upset over something, bucked him off and ran off down the trail. The ranger came over to the man to check him and was horrified to see he was left with only one leg. A leg, boot and all was still in the stirrups of the saddle as they watched the mule hightail it. The poor ranger was beside himself, trying to treat the fellow for shock, explaining how they would get an emergency crew to haul him out for treatment. About that time, the tourist finally got a word in edgewise to tell the ranger that his "spare" leg was up in his car. All anyone needed to do was go get it for him and he'd be right as rain, although with a few bruises!