What was it?
It seemed to come from somewhere in the house.

But how could that be! I was startled enough, however, to get up and slip on some of my clothes and stand with ears astretch for the next train.
It came and passed, and right in the middle of the noise it made I heard again that quick, sharp sound.

This time I was sure it came from somewhere near, and opening my door, I slid out into the hall.

All my lodgers were in but one, a young gentleman who has a night-key.

And most of the rooms were dark, as I can very well tell from the fact that none of the doors fit as they ought to and there is sure to be a streak of light showing somewhere about them if the gas is burning inside.
Everything looked so natural, and the house was so still, that I was going back again when another train swept by and that sound was repeated.