Marking one's toilet territory
 More eloquent people than I have discussed humanity and human instinct on their blogwebs; what marks a society as civilised is the ability of the people to overcome their evolution-borne raw instincts and to sit and ponder what humane course of action is for the common good.
To this wealth of thought and knowledge I must add the following: that this also applies to toilet usage.
When the motions of civilised people result in faecal residue being left on the toilet bowl, they must overcome the urge to mark their territory like common animals, and instead use the brush of enlightenment to remove these primitive tools of their most basal instincts.
Especially if they've had a muck-spreader effect above the rim.