When you're walking through a grassy area, and you accidentally step on a Red-on-Yellow Coral snake, you'll be glad you were wearing your ankle-high hiking boots instead of your birkies. When we used to canoe on the rivers in North Carolina, the lady-folk were always afraid the Water Moccasins would be jumping out of the overhanging trees into the canoes. They swore they knew people it had happened to. Water Moccasins "are" pit vipers.
Rule of Thumb: always protect your big toe, from Cholla or Coral.