"So there was nobody else in the library, not surprising as you weren't open; you were yards away from the counter shelving your Mills and Boons; and the monitor leapt into the air and dived onto the floor? Was there an earthquake?"
"No, you've got it wrong. The cleaner was in at the time."
"And what was she doing?"
"She was in the cellar putting away the vac."
Somehow the monitor survived to skydive another day.