A poisonous water snake found in the southern United States, named for the white interior of its mouth that it displays when threatened.
Cotton (the white material, from Arabic qutun) + mouth (from Proto-Germanic *munthaz). Named descriptively because the snake's open mouth reveals white coloring similar to cotton.
The cottonmouth snake gets its name from a warning display—when threatened, it opens its mouth wide to show the white interior, which looks like a piece of cotton and warns predators 'back off!'
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