I think this is VERY normal for little ones. They're learning about their bodys by experimentation..
Just a side story, when my brother was young he use to do this weird stand on tippy toes an weird hand/finger movement thing, kinda like a strange dance. My mom's sister used to ask my mom if she could come over to "watch" him, because it was the weirdest thing. My mom would constantly be asking the doctor if that was normal and he kept telling her he was fine and that he'd grow out of it, she could reach down and touch him and he'd stop as well. Funny thing is it became way less severe, but now (he's nearly 30 married with 2 kids) whenever he plays video games or computer games that he's really into the hand/wrist thing kinda comes back and he bounces his knee,.. its funny, something I can tease my big brother about because he never quite grew out of it but it's obviously a subconsious way that he channels his excitement/concentration/stimulation or whatever you want to call it! We all have weird quirks!