One of the earliest forms of rails used by the Americans consisted of a
flat bar half-an-inch thick spiked down to longitudinal timbers. In the
process of running the train, the iron was curved, the spikes loosened,
and the ends of the bars turned up, and were known by the name of snakes’
heads. Occasionally they pierced the bottoms of the carriages and
injured passengers, and it was no uncommon thing to hear passengers
speculate as to which line they would go by, as showing fewest snakes’
heads.