garter snake died

[icygirl]

does anyone know what could've happened?

The bite from the rat may have gotten infected or the rat may have caused internal injury to the snake.

In the future, if you feed live, always supervise the tank while the rat is in there. If the snake takes no interest in the rat you need to remove it before the rat can cause damage. Even if a few scratches or bites from a rat are usually not enough to kill a snake, do you really want to risk permanent scars or damage?

I have only seen a snake once with a mouthful of substrate, and it was a young boa who already had internal parasites and was extremely unhealthy and weak. It died shortly afterwards. I figured the eating of substrate was an after-effect of whatever was wrong with it beforehand.