Wild Garter Snake strange behaviour

Question
Hello. I'm in Nova Scotia and I was walking down the road today and found a garter snake in the middle of a dirt road. It was moving around but not quickly getting away. Soon I started to notice it open its mouth upward. It continued moving forward and circling around and I tried to give it space cause it seemed a little slow and scared, but I was worried a car would come. Finally it started to slither backwards, opening its mouth more and more, almost consistently, I thought it was as if it was screaming, but there was no sound. It looked healthy otherwise, but I kept thinking maybe it was dying. Finally a truck came and my husband urged it off the road with a stick, but even in the grass it didn't run away. It just kept doing the mouth open and backward thing. What do you think was happening? I've never seen a snake act like that before.

(As an aside, the truck driver stopped and said he recently found several snakes in a septic tank, which he rescued. I wonder if maybe this was one of those snakes and it had been poisoned or something..)

Thank you for telling me what you think.

Answer
Rhiannon, I love your name. So cool.

I am in Knoxville, TN. The only behavior I ever ever seen like this is a sign of death. There is no way to know the cause, could be natural, could be poisoned. When a snake inverts like that, it is usually the death throws. I have seen it in may species, also sometimes snakes like boas will look up and raise us, this is called stargazing. They are usually deathly ill and it is some kind of response that we do not yet understand.