Soul = Suffering
Christians postulated that horses and slaves had no souls and presumably thus could not even truly feel pain despite how it looked. This meant it was ok to beat them or work them to death. How convenient that this soul was invisible and undetectable. Its existence could be asserted or taken away at whim without evidence. Modern day Christians mistreat whales whose brains are considerably larger than theirs, justified with similar medieval superstition.
~ Roedy (1948-02-04 age:70)