I wrote a small tool to amplify mouse movements. Modern mouses like the Logitech G502 are very sensitive, and can easily pickup vibrations and sound, acting like a microphone.
In the repository is the tool, and a quick video demonstration of capturing audio with a mouse.
This is madness! I love it. I'd thoroughly enjoy an addition to the demo where you play back audio the mouse has captured – I think many would be interested to hear what kind of fidelity gets captured.
It's quite low quality, only 1 Khz sampling rate and not a lot of resolution. I think you could figure out human voice, though.