Talk Out Your Ears on today's Moment of Science.

The North American bullfrog makes its croak in its throat, using its vocal cords. That's the same way we humans make vocal sounds. It projects that croak, however, though its ears.

It has membranes on the sides of its head that resonate with the same frequency as the croak. So when the vibrations come out its ears, these membranes amplify them and send them out. Whatever the frog says . . . or croaks . . . inside its throat gets projected out through the resonating ears, so that it can be heard all over the marsh. Six species of frogs have ears that do this, too. It's a bit like having two bullhorns attached to the side of your head.