probably a combination of not wanting to sit in feces and/or your perception of the events.

One possible course of events is that the snake is sitting in the warm area of the cage until it has a bowel movement. No longer feels the need to bask after passing feces, and decides to check out the rest of the cage and eventually cool down by sitting in the cool area, coincidentally, away from the feces.

Some of the snakes here at the breeding center seem to go to great lengths to avoid poop, some will sit right in it, they are all individuals and their reactions to poopin' are all gonna be different.

-Jen