“I’d forgotten that,” I admitted. “But it was only for a moment.”

“Long enough.”

“Long enough for what?”

Poirot’s smile became rather enigmatical.

“Long enough for a gentleman who had once studied medicine to gratify a very natural interest and curiosity.”

Our eyes met. Poirot’s were pleasantly vague. He got up and hummed a little tune. I watched him suspiciously.

“Poirot,” I said, “what was in this particular little bottle?”

Poirot looked out of the window.

“Hydrochloride of strychnine,” he said, over his shoulder, continuing to hum.