A couple of pics...

[kibakiba]

Mama does that too. She's gotten a hold of my hand before, she didn't bite down hard but she was looking up at me as if she were saying "go fetch me a pinkie right now or I will bite you harder" of course, I did what she said.

[guidofatherof5]

Mama does that too. She's gotten a hold of my hand before, she didn't bite down hard but she was looking up at me as if she were saying "go fetch me a pinkie right now or I will bite you harder" of course, I did what she said.

It must be a universal garter snake move.
Many of my big radixes will do the same thing.
You nailed it.
They look at you and you know exactly what they want.