- If it's closed there's no airflow (as in zero). - So my old cat can wake me up if he's having problems (or as he says, so I can hear his potty song). - So my cat with dementia can stir up the sand in both litter boxes, and then crap on the carpet. - So I can hear hairballs being hacked up (makes it easier to play the game of "find the hairball" each morning).