Maggie: Dad, why do I have hair in my nose?
Dad: It catches the dirt in the air, and the germs, and makes boogers.
Maggie: Why do I need boogers? Can't I cut out all my nose hair?
Dad: No, you can't cut out your nose hair. You need it to filter out all the dust so you don't get sick.
Maggie: What does 'filter' mean?
Dad: It's like when you fart in the shower, and it stinks super bad. That's because you don't have your undies on to filter out the smell.
Maggie: OH! Okay. Thanks dad.
Yep, of all the ways to describe what 'filter' means, it instinctively goes to potty humor. So just be forewarned if you ever come to dinner at our house.