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.