I think this game was intended for a very specific playstyle, which is having one hand on the arrow keys with three fingers. That might've explained why there were hands in the mix.
So I remember playing this one when I was younger, it was based off one of the Fairly odd parent specials called "school's out the Musical". It was also on the official Nickelodeon website. You had to hide behind the mailbox and stuff when the gray pixie fairies were on screen or else they turned you boring and temporarily prevents you from entering a level. There were also a few other rhythm flash games that I used to play such as the Johnny bravo rhythm game and Grim adventures of Billy and Mandy "Zap To It".
YO I REMEMBER THIS This was one of my first rhythm games, along with Gamehouse's Tap a Jam, which was a banger and actually pretty challenging. Please do check it out if you can