The Song of the Mice

Physorg notes that there is research going on about how mice sing (ultrasonically):

Whether or not mouse song involves learning either through auditory imitation or behavioral feedback (e.g., from the mother)... is a subject of hot debate, and the answer is proving elusive. To highlight the difficulties facing researchers, two studies published on March 9, 2011 in the open-access journal PLoS ONE have come to differing conclusions about whether mouse vocalization patterns are innate or learned.

Rodents sing and they laugh. Sound like good company, really.