The late George T. Angell, in "Our Dumb Animals," gives this incident, showing that fear of unseen authority, is a forcible motive, even with would-be transgressors:

The incident occurred on the rise of land near Park Street Church (Boston). A horse, evidently laboring under the impression that he was overloaded, stopt and refused to go any farther, and a crowd gathered. Just then one voice called out from the crowd:
"Why don't you whip him?"
"Whip him," said the driver--"whip him! How do I know that there ain't an agent of that darned old Society for the Prevention of Cruelty to Animals standin' right here in this crowd?"
We have never considered it good policy to send out any of our agents in uniform, and so any respectable citizen who seems to be interested in the protection of horses is liable to be suspected of being one of our agents