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Cottonmouth Snake

Photo: Cottonmouth snake
Water moccasins, like rattlesnakes, are pit vipers—they have heat-sensitive organs between their eyes and nostrils which helps them track prey. When threatened, water moccasins will open their mouths wide as a warning, a defensive behavior also displayed by non-poisonous water snakes.
Photograph courtesy Matthew Perry/U.S. Fish and Wildlife Service

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