Rex grimaced. "Really?" But he took the list, his face scrunching into a small frown as he read the ingredients at the bottom. "Castor oil, unicorn horn..." Okay, those were easy enough. But - he squinted and held the paper closer to his face.

"What's a bezoar?"

The shopkeeper - who'd already picked out the other two ingredients and laid them on the counter for him - produced a small box full of round objects that looked like rocks. "It's a stone from the stomach of a goat," he explained. "Commonly used in poison antidotes."

Rex took the box, blanching a little at its contents. "Are you telling me a goat barfed these up?"