Wearing protection

"Do you have an extra set of earplugs?"
"I left the other nice ones at home, but I have the foam ones."
"Okay. Did you get that other pair for me or for you?"
"Well, both...in case one pair gets nasty, or if I lose one."
"Oh, ok."
"Of course, if we only had three, you could stick two in your ears and one in your belly button."
"My belly button?!"
"Sure, to protect the hearing of our future child..."