What is it that makes a dog "thump" with his leg when you scratch that right spot?

I've wondered this myself. It appears that the "right spot" is one that generally itches and feels good to get scratched. The thumping seems to be a reflex because dogs scratch with their legs, usually in a similar motion to the thumping motion.

So it looks to me that, when you scratch the dog in a spot that itches, the dog moves its leg in the same way it would if it were scratching itself.

I would assume its like a "tickle-ish" spot. Mine does the same thing, only he really LOVES his butt scrated and he will just sit there with his head all up in the air looking so happy!! But hey, who wouldn't want their butt scratched- right?? :)

Assuming you are asking a legitimate question, ours does the same thing.........right under her ribs...........and she'll back up to my hand to have her back scratched right near her tail, they cant reach it like we humans can............come to think of it i cant scratch my back very well eitiher.........go figure............now where did i put that back scratcher????? have fun, sharon t. from ohio

I assume it's sheer joy. My husband does something similar when I scratch his back.

What is it about humans that makes us laugh when you touch certain 'ticklish" spots?