Super-sonic listening

One of the circuits I made in my Basic Analog Circuit class was a electret microphone amp that  can have almost infinite gain. It samples itself and regulates the gain based on the input. In a quieter environment the gain can become so high that it is possible to hear things that normally the human ear cannot hear.

The ITP floor is quite noisy so nothing too out of the ordinary presents itself, though some sounds are much louder than normal: 

The wooden mirror sound really interesting, though the general noise from the busy floor interferes: 

I then went into the stairwell to try to find a quieter place. I had just eaten some almonds and was moving my tongue around in my mouth, and I could hear all the sounds in my mouth! Here is a recording, the mic was no where near my mouth, it sounds sort of crazy: 

I then went into the back stairwell, where there are some interesting oscillations going on: