My niece does as a result of spending too much time in a baby walker. But I would say that if his heels are hurting get it checked. Has he always done it? Or is it a new thing? I would say if its a new thing, has there been a change in the family / routene / in his world which might have unsettled him and might make him attention seek? Making him act out, children can do the oddest things to get attention. If he's always done it, it might need treating and the earlier you check and get help the better. At what age did he walk? They can do alsorts to help walking issues, but it depends whats happening. Do his muscles around the ankle seem tight?