This is a recording of mice singing. I wanted to check if it is still possible to embed sound in these posts, so I chose this sample, which reminds me of the Clangers! The mice are really much higher in pitch and the frequency has been lowered so humans can hear it, similarly to how bat detectors work.

Download this audio clip.Audio player: audioS1.mp3

Source http://www.nature.com/news/2005/051031/multimedia/audioS1.mp3 (needs Quicktime)