That is weird… normally I would say that if the parents aren’t worried that it’s not a problem… but that doesn’t sound good. If she is so tense that it is hard to move her arms or legs and she does that ‘humping motion’, than she might need to go to a doctor…
Does she do it every time she gets tired or is it just once in a while?
Does she draw her legs up to her stomach?
Are her hands clenched tightly?
Does she appear to be in any pain?
Oh, and that could be an early symptom of autism… ask her parents to hold off any more vaccinations or immunizations until she’s older. They can cause autism (several different families we know have had that happen to their children recently).
i did that when i was a baby. the doctors said it was normal and i did it until i was like 5. it was the only way for me to fall asleep. they called it rocking myself. and my sister made fun of me for “humping the floor” but its nothing to do with humping. its just a comfort thing.