What's something weird and mostly useless that you can do with your body?

Same! I liken it to a knock off version of Mongolian Throat singing.

Ah yes, multiphonics.

I love doing this because it sounds like you're charging a laser weapon

Lol I just tried that to see how it works.

It's hard because if you close your lips too much to whistle it restricts the airflow and kills the hum.