Regular

“It moves about?” said the possible professor.
“Oh, yes. Everywhere,” said Rincewind.
“I know of no plant life that moves about!”
“Really? I wish I didn’t,” said Rincewind, fervently, gripping the man a little tighter. “Come on, after a nice warm drink you’ll–”
“I must examine it closely! I am aware, of course, of the so-called Venus Fly–”
“Please don’t!” Rincewind pleaded, pulling the man back. “You cannot botanise the Luggage!”

– not more than once, anyway |
Terry Pratchett, Ian Stewart, and Jack Cohen, The Science of Discworld III: Darwin’s Watch