Murphy and O'Reilly, two Irish gents, are walking through a forest, and they come upon a very, very, very deep well. They are curious as to how deep the well is, and to measure it, they decide to throw a stick down and count how long it takes for the stick to hit the bottom.
They take a log and throw it into the well, and begin to count. A minute later, a goat runs up and jumps in the well. They naturally consider this strange, but continue counting regardless of the weirdness of a goat jumping down a miles-deep well.
After a little while, a farmer comes up to them and says, "I'm missing a goat! Have you seen one?"
They reply, "Well, a few minutes ago, a goat came along and jumped into this well."
"Oh," said the farmer. "Well, it can't have been one of mine. Mine were all tied to logs."