After the flood, Noah brought his ark to rest on Mount Ararat. The animals started debarking: two elephants walked off, then two lions, and then two camels. Next, four gnus came down the gangplank.
Noah's wife was watching and she asked him, "I thought you brought only two of each animal?"
"Well, you see," explained Noah, "first there's the good gnus and then there's the bad gnus."