Pygs do have HUGE fangs when they are born compared to their bodies. I think their fangs are full size and they grow into them
And as Chuck said, they are born fully hot. Additionally, they are not able to meter their venom yet, so generally a bite from a young venomous snake results in a full envenomation. I don't remember many instances of dry bites from neos or juvies. Especially if the snake bit several times.
They prolly killed some poor gray ratsnake.