^* Because the astronauts’ time was rigidly scheduled and because bowel movements generally can’t be, crew members were forced into conversations like this one, in the Apollo 15 mission transcript, between Commander Dave Scott and Lunar Module Pilot James Irwin.

SCOTT: Al, why don’t you and I switch off here when…
IRWIN: I’d like to take a crap if I can work it in, Dave.
SCOTT: Okay.
IRWIN: Tell me when.