D: Okay, today I'm going to do something unusual.

Y: Oh yeah? This should be fun.

D: I'm going to deliver today's Moment of Science entirely through my ears. (MMM-      MMM-MMM SOUNDS.)

Y: Oh, stop that. You can't make sounds out your ears.

D: Why not? Bullfrogs can!

Y: Bullfrogs make sounds that come out their ears? Don't you mean their mouths?

D: I mean their ears. 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.

Y: How on earth does it do that?

D: 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.

Y: Or two "bullfrog" horns.

D: Exactly!  

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