I have a pair of Drymobius and I noted that a bite involved a rather significant bleeding. I'm going to look teeth, but i think it's not a rear fang snake.
So it seems that Drymobius have a saliva involving a bad coagulation. Is it Duvernoy's gland or saliva gland? It really clear when they feeding, the prey bleed a lot. I never observed bleeding on prey of heterodon.