"Hiking Boys and the Goat" joke

There were these two guys out hiking when they came upon an old,
abandoned mine shaft. Curious about its depth they threw in a pebble
and waited for the sound of it striking the bottom, but they heard
nothing. They went and got a bigger rock, threw it in and waited.
Still nothing. They searched the area for something larger and came
upon a railroad tie. With great difficulty, the two men carried it to
the opening and threw it in. While waiting for it to hit bottom, a goat
suddenly darted between them and leapt into the hole!
The guys were still standing there with astonished looks upon their
faces from the actions of the goat when a man walked up to them. He
asked them if they had seen a goat anywhere in the area and they said
that one had just jumped into the mine shaft in front of them! The man
replied, "Oh no. That couldn't be *my* goat, mine was tied to a
railroad tie."