He could scarcely keep his eyes open.

Presently, although he never moved a muscle of his back and sat up stiff and straight as a poker, he was sound asleep, and the reins in his grasp slipped lower and lower and lower.
The horse was an old one, stiffened and jaded by much hard travel, but it had been a mettlesome one in its younger days, with the recollection of many exciting adventures.

Now, although it seemed half asleep, dreaming, maybe, of the many jaunts it had taken with other American tourists, or wondering if it were not time for it to have its noonday nose-bag, it was really keeping one eye open, nervously watching some painters on the sidewalk.

They were putting up a scaffold against a building, in order that they might paint the cornice.
Presently the very thing happened that the old horse had been expecting.

A heavy board fell from the scaffold with a crash, knocking over a ladder, which fell into the street in front of the frightened animal.