I have scientifically named this "Popcorn Butt." :)
When I would get home from a brisk neighborhood walk (when I was still able to walk briskly--can't anymore), and after sitting still for a minute or so, the muscles all across my rear and hips would start "jumping" or twitching randomly, like popcorn popping.
This would last for a minute or two and then die down.
What gives?? Is this normal after exercise?? Anyone else experience this?