That can only be answered by a professional who sees your child do it, or runs tests for possible problems which you don't want to subject your child to test that may prove to be pointless. It is possible that your son is just expressing himself in a way that you don't understand. Try video taping your son doing this behavior and showing that video to his physician and possibly a psychologist. See what they say.
The sorts of repetetive behaviours you describe may be indicative of an autistic spectrum disorder. Consult a health proffessional.
forwards and backwards
forwards and backwards
backwards
vertical
Frequency matched. Basically, the movements of the shaft ie backwards and forwards during impact are all the same.
Words that are the same forwards and backwards are called palindromes.
None are but what cities/towns are spelled the same backwards and forwards?
You skip backwards when you jerk.
a ton. ton backwards is not
forwards
Forwards
Backward.