You really can't argue with the reasoning of a three year old.
Noah - in a spurt of tidyness and helpfulness - decided to tidy away his yoghurt carton and spoon. Former to the bin, latter to the cutlery drawer. When I spotted him, I thanked him for his help but asked could he put the spoon in the kitchen instead (what kitchen!?!) to be washed.
Looking round he informed me that it was OK because he had licked it clean. Drawer shut. Job done. Walk away.
Hmmmm...