I am just putting out possibilities of behaviors that I see that usually involve either feeding in captivity or feeling threatened. I know that FR has much more experience with specifically Heterodon nascius as I only have one and can thereby only make so many observations. He keeps several from my understanding and also studies them in nature on a regular basis it seems so he may be able to identify it as something else. If you can post a link to a youtube video of the behavior that would help at least me a great deal in seeing what exactly the behavior is like.

I can't make a clear judgement of my thoughts on it without seeing it as you have expressed it to be an active behavior. Seeing it allows a more detailed understanding of what is actually going on than mere description when it comes to things such as this.