Intracensor

The other day, at Corporate Choir rehearsal, I was listening to our director give us, well, direction, and I heard a hissing noise coming from the vent.

GDad: Is that [Pauses and does some calculations about the amount of funny in this statement.  There are about 30 people in the room.  Three of them might get the reference.  Of those three, one might think it's morbidly funny, and two will be offended enough to express their displeasure.  The rest of the statement is subvocalized instead of vocalized.] Zyklon-B?