The Apollo 10 crew practices in a simulator command module before the mission.(NASA)
During Apollo 10 — in which a crewed spacecraft orbited the moon as a dress rehearsal for the first lunar landing — astronauts encountered a deep mystery.
"Oh — who did it?" commander Tom Stafford suddenly asked, six days into the mission, as the crew discussed preparations for leaving the moon's orbit.
"Who did what?" inquired command module pilot John Young.
"Where did that come from?" interjected lunar module pilot Eugene Cernan.
A moment later, for listeners at ground control, the mystery was resolved.
"Give me a napkin quick," commanded Stafford. "There's a turd floating through the air."
It sounds apocryphal, but it's the truth: in an era when spacecraft waste management consisted of "a plastic bag which was taped to the buttocks to capture feces," turds could escape from time to time and float about the spacecraft.