"System?" said Hewitt, with a shrug of the shoulders, an hour or two after
in Sir James' study. "I can't say I have a system. I call it nothing but
common-sense and a sharp pair of eyes. Nobody using these could help
taking the right road in this case. I began at the match, just as the
Scotland Yard man did, but I had the advantage of taking a line through
three cases. To begin with, it was plain that that match, being left there
in daylight, in Mrs. Cazenove's room, could not have been used to light
the table-top, in the full glare of the window; therefore it had been used
for some other purpose--_what_ purpose I could not, at the moment, guess.
Habitual thieves, you know, often have curious superstitions, and some
will never take anything without leaving something behind--a pebble or a
piece of coal, or something like that--in the premises they have been
robbing. It seemed at first extremely likely that this was a case of that
kind. The match had clearly been _brought in_--because, when I asked for
matches, there were none in the stand, not even an empty box, and the room
had not been disturbed. Also the match probably had not been struck there,
nothing having been heard, although, of course, a mistake in this matter
was just possible. This match, then, it was fair to assume, had been lit
somewhere else and blown out immediately--I remarked at the time that it
was very little burned. Plainly it could not have been treated thus for
nothing, and the only possible object would have been to prevent it
igniting accidentally. Following on this, it became obvious that the match
was used, for whatever purpose, not _as_ a match, but merely as a
convenient splinter of wood.

"So far so good. But on examining the match very closely I observed, as
you can see for yourself, certain rather sharp indentations in the wood.
They are very small, you see, and scarcely visible, except upon narrow
inspection; but there they are, and their positions are regular. See,