First, the scientists had to figure out if the frogs could even hear, so they recorded calls from other frogs and played them through speakers. The test frogs responded, indicating that they can indeed hear. But x-rays showed that the frog's bones weren't conducting the sound (as our own jawbones do), nor were the muscles or organs of the frog. So the scientists hit the computers and ran a simulation: what if the frog's mouth was directing the sound to the inner ear, a cavity within the frog's skull that hosts reverberated noises. And it worked! The math showed that this method could indeed allow the frog to "hear."