The Cottonmouth (which used to be called Cottonmouth Moccasin or Water Moccasin) is a venomous, semi-aquatic snake. It is one of the five species of pit viper that inhabits Louisiana. It is also the only semi-aquatic viper in the world. The name, Cottonmouth, comes from the way the inside of the mouth is white and looks like cotton. When cornered, they open their mouth to display the "cotton" as a defense mechanism, but would rather just be left alone.