A group of researchers from MIT, Microsoft Research, and Adobe Research are experimenting with seemingly inanimate objects as a proxy for sound in the vicinity. They call it the Visual Microphone.
When sound hits an object, it causes small vibrations of the object's surface. We show how, using only high-speed video of the object, we can extract those minute vibrations and partially recover the sound that produced them, allowing us to turn everyday objects—a glass of water, a potted plant, a box of tissues, or a bag of chips—into visual microphones.
See the demo in the video above. It's impressive. It's also great that there's another use for high speed video other than watching water balloons pop and guns fire on the Discovery Channel.