It's kind of fun seeing the spontaneous cooperation that occurs between two (or more) random people on the internet.
I was just minding my own business, getting a feel for all the notes of each instrument. I found an instrument that I liked and was just slowly moving back and forth from the top to the bottom, when suddenly I realized that another player was mirroring me. He (or she) would try to stay synced with me, but on the opposite end of the screen as me.
We did that for several measures until I ruined everything by deciding to try out more instruments.
It was pretty cool.