Dennis opened the knife and laid it in the palm of his hand. I stood still and watched him. "You've sharpened pencils with this knife and the pencils have left their mark. If you hold the knife as you would when sharpening a pencil and look down on the blade there are no pencil marks visible. Now turn the knife over and you will find the marks on the other side of the blade." "Half a minute," I said eagerly, "let's have a look. The knife is in position for sharpening a pencil and the back of the knife is pointing to my chest. The marks are underneath." I took a pencil from my pocket and tried it. "Yes, I've got you, Dennis. It's quite clear. If I held the knife with the point to my right instead of to my left, as I should do in sharpening with my left hand, the marks appear on the other side of the blade. It is not quite conclusive, Den, but it's jolly cute." "Not when you're looking for it," he said. "I was struck by the fact that the knife which, by its size and weight, was a seaman's handy tool, had also been used for the repeated sharpening of a blue pencil. When I saw those indications I went through the motion and came to the conclusion that the marks were on the wrong side. Then I tried with my left hand and accounted for it. The blue pencil made me suspicious. I have no knowledge of a yacht-hand's duties, but surely sharpening blue pencils is not one of them. Then the knife had also been carried in the same pocket as a piece of white chalk. The only sort of person I could think of who would carry a piece of chalk loose in his pocket and use a blue pencil continuously was a schoolmaster. So I stated definitely--there's nothing like bluff--that the knife belonged to the left-handed man, who quite obviously had red hair, who appeared to wear the insignia of the married state, and who--again according to the law of averages--had at least one child. I naturally slumped the schoolmaster idea in with it, and there you have the whole thing in a nutshell. But it was Garnesk who set me looking for left-handed clues, and if I hadn't been looking for it, it would never have entered my head." "But look here," I suggested, "some people sharpen pencils by pointing the pencil to them. Wouldn't that produce the same effect?" "Yes," he admitted, "I thought of that. But the marks would have been very much fainter, because there would have been much less pressure. I put that idea aside." "Good!" I exclaimed. "I should much prefer to swallow your theory whole, Dennis, but it struck me that might be a possible source of error, which, of course, might have led us on to a false trail. And, I say, those questions you asked about the time he stayed in port and the hotel. Were those all bluff? Or had you some sort of idea at the back of them?"