Which type of snake's mouth is white when opened?

The correct answer is Cottonmouth, which is a type of water moccasin. When a Cottonmouth opens its mouth, it displays a distinctive white interior, which is a notable characteristic used to identify the species. This white coloration serves as a warning sign to potential predators or threats, making them more noticeable when the snake feels threatened.

The other snakes listed do not exhibit this particular trait when their mouths are opened. For example, Copperheads have a more neutral-colored mouth, while Coral snakes typically have a more vibrant color pattern, and Rattlesnakes exhibit a range of colors but do not show the striking white interior associated with the Cottonmouth. Understanding these differences can be crucial for identification and safety in the field.