Here is exactly what happens, IF the rat had a pile of chow and a water bottle, it never would have turned on the snake.
Rats need a steady supply of food and water.
Mice and rats locked in a box will turn on each other when denied food from any other source.
When I was breeding mice and rats for my own use, all it took was one night of falling asleep before filling their food bowls and by the next morning one of the rats was dead and stripped down to a skeleton and some fur on the ground.
I am in no way condoning what happened, but I know exactly WHY it happened, had the keeper provided something for the rat to eat, a pile of cereal, dog food or a biscuit, the rat would have preferred that over eating snake flesh.
want to see a cool demonstration? lock a solo rat in a fish tank for 24-48 hours with no food and water, now, go stick your hand in there...