"And he probably looked into Number Six through the first hole while Martinez was boring the second. I suppose you can tell which of the two holes was bored first?" chuckled Tignol.
M. Paul started, paused in a flash of thought, and then, with sudden eagerness: "I see, that's it!"
"What's it?" gasped the other.
"He bored this hole first," said Coquenil rapidly, "it's the right-hand one when you're in this room, the left-hand one when you're in Number Seven. As you say, the murderer looked through the first hole while he waited for the second to be bored; so, naturally, he fired through the hole where his eye was. That was his first great mistake."
Tignol screwed up his face in perplexity. "What difference does it make which hole the man fired through so long as he shot straight and got away?"
"What difference? Just this difference, that, by firing through the left-hand hole, he has given us precious evidence, against him."
"How?"
"Come back into the other room and I'll show you." And, when they had returned to Number Seven, he continued: "Take the pistol. Pretend you are the murderer. You've been waiting your moment, holding your breath on one side of the wall while the auger grinds through from the other. The first hole is finished. You see the point of the auger as it comes through the second, now the wood breaks and a length of turning steel shoves toward you. You grip your pistol and look through the left-hand hole, you see the woman holding back the curtains, you see Martinez draw out the auger from the right-hand hole and lay it down. Now he leans forward, pressing his face to the completed eyeholes, you see the whites of his eyes, not three inches away. Quick! Pistol up! Ready to fire! No, no, through the left-hand hole where he fired."
"Sacré matin!" muttered Tignol, "it's awkward aiming through this left-hand hole."
"Ah!" said the detective. "Why is it awkward?"