It should work for anything conductive, I just thought tea would be humorous (variation: aluminum shot glass). I bet Jello would work since it's mostly water.

Not even a bottle of water? Find some dead headphones from a friend, cut the wire, and you're set -- the rest is just software :)

The main epiphany was that 44100 Hz (standard audio sampling rate) is evenly divisible by 60 Hz (mains power frequency). Beyond that, I'm pretty sure it was just the tea.

I'll have to stick with the tea.

Ah yes amazing. Perhaps that will be my next feat, attaching multiple channels to beer pong cups?

Doesn't matter, you just need some kind of conductive substance. I was using a tea from mighty leaf, if you're super curious :)

That would be really neat if our electromagnetic fields had such a strong effect on fluids!

One way I think of it is that our body acts like an antenna, and the wire + tea acts like an antenna. Our body is grounded to an electrical "plane" that is vibrating at 60 Hz or 50 Hz, and as we get closer to the wire we "transmit" (are capacitively coupled with) the wire + tea. Check out the original -- the theremin -- for more info on the theory. I really only have a strong intuition for the ideas, and not a scientific understanding.