Rail listeners

Trains of cars were heard coming in and going out of Corinth constantly. Some of the men who had been engaged in various capacities on railroads before the war claimed that they could tell, by putting their ears to the rail, not only which way the trains were moving but which trains were loaded and which were empty. They said loaded trains had been going out for several days and empty ones coming in. Subsequent events proved the correctness of their judgment.

That’s U. S. Grant, in his memoirs, talking about skillful rail listeners outside Corinth Mississippi, 1862.