Notes　Scene 58: Holmes Explains

The idea of a snake instantly occurred to me, and when I coupled it with my knowledge that the doctor was furnished with a supply of creatures from India, I felt that I was probably on the right track. The idea of using a form of poison which could not possibly be discovered by any chemical test was just such a one as would occur to a clever and ruthless man who had had an Eastern training. The rapidity with which such a poison would take effect would also, from his point of view, be an advantage. It would be a sharp-eyed coroner, indeed, who could distinguish the two little dark punctures which would show where the poison fangs had done their work. Then I thought of the whistle. Of course he must recall the snake before the morning light revealed it to the victim. He had trained it, probably by the use of the milk which we saw, to return to him when summoned. He would put it through this ventilator at the hour that he thought best, with the certainty that it would crawl down the rope and land on the bed. It might or might not bite the occupant, perhaps she might escape every night for a week, but sooner or later she must fall a victim.

蛇という考えがすぐに頭に浮かんだ。博士がインドから取り寄せた生き物を手元に置いていることとあわせて考えると、これはおそらく正しい筋をたどっているのだと感じた。化学検査ではどうやっても見つからない種類の毒を使うという思いつきは、東洋仕込みの、頭の切れる冷酷な男にこそ浮かぶものだった。そのような毒が効くまでの速さも、彼の立場から見れば利点にちがいなかった。毒牙が仕事をした跡を示す、小さな暗い二つの刺し傷を見分けられる検死官がいるとすれば、よほど目の鋭い人物だろう。それから私は口笛のことを考えた。もちろん、朝の光が犠牲者の目にそれをさらす前に、博士は蛇を呼び戻さなければならない。博士は、おそらく私たちが見たあのミルクを使って、呼ばれたら自分のもとへ戻るよう蛇を仕込んでいたのだろう。博士は、これぞと思う時刻に、この通風口から蛇を送り込む。紐を伝って下り、ベッドに降り立つと確信したうえでだ。蛇が寝ている者に噛みつくかどうかはわからない。おそらく一週間、毎晩難を逃れることもあるだろう。だが遅かれ早かれ、犠牲者にならざるをえない。