My Cats Clean Their Litter Box

I have two of the funniest cats in the world. They are nothing short of amusing entertainment! They have a strange but entertaining habit of cleaning their litter boxes. Yes, I mean cleaning them from top to bottom after using them. I don’t mean the usual “covering up” after their business is done. They stay in the box several minutes afterwards and scratch at every spot of the box and then the lid. They both do it as if they know the other is watching and don't want to miss anything in case it is spot checked. When they have completed the task, they each step out of the box and look back as if admiring their handiwork.