Shaking

Hello,

I have a Mississippi map and a yellow bellied terrapin that are roughly 5 months old. We have noticed that the yellow bellied terrapin tends to flick his front and back claws when he is basking. he also shakes his head. He doesn't appear to have any swelling or open sores. No discolored skin or shell nor is he shedding. He is eating normally and as well as swimming about as well as interacting with our other terrapin. I have searched high and low on the net and cannot find anything about this behavior. I do not believe it is mating as he is a bit young and it is not directed at the other turtle. I am not severely worried as he looks healthy. I am just interested to know what this behavior is!

Thanks a bunch!
Lacey