Phillip Yancey, What's So Amazing About Grace, Zondervan, 1997, p. 33
Mark Twain used to say he put a dog and a cat in a cage together as an experiment, to see if they could get along. They did, so he put in a bird, pig and goat. They, too, got along fine after a few adjustments. Then he put in a Baptist, Presbyterian, and Catholic; soon there was not a living thing left.