Here is a question I was asked by a new snake owner: There is a big hole in my snake's mouth. The snake is eating well and seems healthy. It is not the throat but is on the bottom of the mouth. What is it?
Answer: The hole you are seeing is the glottis. It connects to the windpipe. It is like a spring covered with flesh. When your snake is eating the glottis is pushed forward and the cartilage rings (the spring) holds the glottis open. Your snake is now able to breathe while swallowing its food. Without this hole, the snake would choke. There is a small piece of cartilage in the glottis that allows the snake to make the hissing sound when the air is forcefully expelled. I hope this explains the hole in your snake's mouth.