There was a guy in the lab the other day calibrating the balances. He saw me taking my marbles from a beaker and putting them on top of little test tubes. He said, (very earnestly) "Do you test marbles here?"

I thought about saying, "Yeah, you know I'm quality control to make sure they are round enough, glass enough, that the cat eye is catty enough, stuff like that."

(my fleeting thoughts)

Instead I said, "No, I just use these as stoppers so my liquid doesn't evaporate when I heat it up."

It's not nice to make strangers feel dumb.
Making friends and family feel dumb is A-okay.