Missing scales?

[Bcycling]

I think what you are actually seeing is where the scales naturally split apart so the skin can stretch. Once the mouse is swallowed does the spot of 'missing scales' disappear?

I'm not 100% on that idea, but I think I've noticed a 'line' on the underside of my snakes mouths that could be a natural stretch point.

Thats what I was thinking also. I just think most people don't see that part of the mouth when they are eating