Is it a good idea to scratch my dog's chin until his leg vibrates like he is itching the ground?

I think you might be giving that dog a seizure!

it is not a seizure. I believe it is an automatic response.

I think they like it. If they are putting their head back and sorta panting and their tongue hanging…then I think they like it…maybe? I don’t know I agree with @jazmina88 maybe it’s like how their tails wag.

My dogs love it. They close their eyes with pleasure, and if I stop petting them, one of them will nudge my hand to get me to start again!

When dog do that they are loving life. It’s like your that is the spot. Keep rubbing.

Since you are scratching a nerve and the response is automatic it could be annoying if you continue it for long. Dogs do love scratching however so move your hand over a bit to let the dog enjoy the experience without jerking his leg.

Pet and scratch your dog as much time will allow!

I know that dogs love being scratched. I’ve had dogs my entire life.
What I am asking is regarding the spot that makes their leg move when you scratch. Every dog has this spot. I just happen to have two dogs that have nothing but this spot.

Yes! And as often as possible!!!
Under the collar is a great spot, too!