Well, I knew it. It turns out that mice sing
, probably to attract mates. Timothy Holy and Zhongsheng Guo of Wash U. in St. Louis put male mice in a teeny tiny sound booth
along with cotton swabs soaked in (presumably hot) female mouse urine. The little hombres started crooning away, at ultrasonic frequencies, of course, and their songs show surprising structure. You can hear slowed-down recordings fit for human ears (ladies, don't get excited now) here
, although I'm told that this is best done with cats in the room since it drives them absolutely bonkers.