“Well, I can’t explain it, whether it’s something in the actual eye, or something in the brain, or what, but I have got rather an uncanny habit of recording things unconsciously. You know that game where you look at a tray full of small objects for three minutes, and then turn away and try to make a list of them. It means a devil of a lot of concentration for the ordinary person, if he wants to get his list complete, but in some odd way I manage to do it without concentration at all. I mean that my eyes seem to do it without the brain consciously taking any part. I could look at the tray, for instance, and talk to you about golf at the same time, and still get my list right.”

“I should think that’s rather a useful gift for an amateur detective. You ought to have gone into the profession before.”

“Well, it is rather useful. It’s rather surprising, you know, to a stranger. Let’s surprise Cayley with it, shall we?”

“How?”