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Holmes explains how Helen's account had already led him to expect a ventilator before he saw the room. The clue lay in the sequence of events she described. He then points out a curious correspondence between the dates of several changes at the house and asks Watson to think through its significance.
"Oh, yes, I did. You remember in her statement she said that her sister could smell Dr. Roylott's cigar. Now, of course that suggested at once that there must be a communication between the two rooms. It could only be a small one, or it would have been remarked upon at the coroner's inquiry. I deduced a ventilator."
「ああ、分かっていたとも。彼女の話に、姉がロイロット博士の葉巻の匂いをかげたとあったのを覚えているだろう。となれば当然、二つの部屋の間に通じるものがあるはずだと、すぐに思い当たる。それは小さなものでしかありえない。さもなければ検死審問で言及されていたはずだ。そこで私は通風口だと推理したのだ」
"But what harm can there be in that?"
「だが、それのどこに害があるんだい?」
"Well, there is at least a curious coincidence of dates. A ventilator is made, a cord is hung, and a lady who sleeps in the bed dies. Does not that strike you?"
「そうだな、少なくとも日付に妙な一致がある。通風口が作られ、紐が吊るされ、そしてベッドで眠る女性が死ぬ。これに何か思い当たらないかね?」
"I cannot as yet see any connection."
「まだ何の関連も見えないが」
"Did you observe anything very peculiar about that bed?"
「あのベッドに、とりわけ変わったところに気づいたかね?」
"No."
「いや」