How do snakes hiss if they don't have front teeth?

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Dogs say "woof," cats say "meow" and snakes say "sss." To make this sound, humans have to position their tongues against their front teeth. Snakes don't have front teeth, so how can they make this sound — and sometimes even stick out their tongues at the same time?

It turns out that snakes make that hissing noise a bit farther back in the respiratory system than we do, in a structure called the glottis. The glottis is a tiny opening at the bottom of the snake's mouth that opens when the snake breathes.

The glottis is connected to the trachea, or windpipe, which itself is connected to the snake's lung. Snakes have only one functioning lung; the other is vestigial, meaning it’s now a small remnant of a larger, functional organ that existed in the snake’s evolutionary ancestors. The functioning lung is made up of two parts.

"There's the vascular lung; that's what our lungs do, so it absorbs oxygen and things like that," David Penning, an assistant professor of biology at Missouri Southern State University, told Live Science. "The back half of the lung is what's called the saccular lung, and it's basically like an old-timey fireplace bellow. It's just an empty balloon for nothing but just holding air."

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