I've studied this for sometime and have worked out what is happening.
You start off with a corn snake, small tank/UTH
corn grows up and moves on to bigger tank.
what you going to do with the empty tank?
It calls to you in your sleep! "fill me! fill me"
So you go out and get a king snake and whilst your there you pick up a royal python and another small thank.
They both grow up and your left with 2 small empty tanks.
They then start to call to you in your sleep! the circle or snakes beggins again.
Preserve Wildlife Pickle a Squirrel