Mice Make Ultrasonic Sounds
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.