Mice are able to make ultrasonic “songs” to attract mates as well as help them defend their territories. The sounds are high frequency whistles, and are completely inaudible to the human ear. Until now, it was not known how the mice were making these sounds.
It turns out they are making the sounds in a way never seen before in any animal—they shoot air from the windpipe against the inner wall of their larynx. This causes a resonance and produces the ultrasonic “whistle”.
The only thing that has been known before to make these high frequency sounds is the engines of supersonic jets. It is possible that other animals, including bats, may be using the same mechanism.