Dinosaur

"For he'd snatched a coupling at the brake to make a plaything of the guard"

"For he'd snatched a coupling hit the brake to make a plaything of the guard"

On a loose coupled train the links between wagons were large 3 link chains that had a bit of slack. If an engine started briskly it would take up the slack wagon by wagon and on a long train the engine could be moving relatively quickly by the time the brake van (caboose for the transatlantics) started moving at all. If the driver had applied the brake in the meantime the wagons would continue to bump into each other until the brake van hit the now stationary train, shaking up the guard.

The sound of a loose coupled train was distinctive and common but now almost lost to the world, along with "fly shunting" where wagons were uncoupled in ones, twos or more then given a push to make them roll away into the sidings without the rest of the train having to follow. By use of a number of sidings trains were split up and sorted quickly at hubs (or marshalling yards) according to their onward destination.

rather like this - fly shunting