Hi there,
Welcome to the forum!
Your question is a good one but it's really in the wrong place. If you'll put questions like this in the General Care section you'll be more likely to get replies. What you should post here ("Hi! Introduce Yourself Here") is info about yourself and your turtle like - how long have you had him/her? What's his/her name? how did you get him/her? We're very interested in people and their turtles!
Now to your specific question. I agree with DavidY - it's probably just normal male turtle behavior. That business of shaking the front toenails is either part of a mating ritual or aggression. Sometimes females do it too. It's interesting, isn't it.
When a male turtle matures his tail gets a lot longer and thicker. Does your turtle's tail look something like this? If it does, it's normal:
