“Could the strychnine have been administered in Mrs. Inglethorp’s after-dinner coffee which was taken to her by her husband?”
“Possibly, but strychnine is a fairly rapid drug in its action. The symptoms appear from one to two hours after it has been swallowed. It is retarded under certain conditions, none of which, however, appear to have been present in this case. I presume Mrs. Inglethorp took the coffee after dinner about eight o’clock, whereas the symptoms did not manifest themselves until the early hours of the morning, which, on the face of it, points to the drug having been taken much later in the evening.”
“Mrs. Inglethorp was in the habit of drinking a cup of cocoa in the middle of the night. Could the strychnine have been administered in that?”
“No, I myself took a sample of the cocoa remaining in the saucepan and had it analysed. There was no strychnine present.”
I heard Poirot chuckle softly beside me.
“How did you know?” I whispered.
“Listen.”
“I should say”—the doctor was continuing—“that I would have been considerably surprised at any other result.”
“Why?”
“Simply because strychnine has an unusually bitter taste. It can be detected in a solution of one in seventy thousand, and can only be disguised by some strongly flavoured substance. Cocoa would be quite powerless to mask it.”