Roger writes:
They say that the Incas used to perform frequent human sacrifices to the sky gods, with the objective of praying for rain and preventing droughts. These sacrifices were accompanied by horrific and grotesque rituals and cruelty. If, despite these excesses, the drought came anyway, then the priests advised the people that there had been insufficient sacrifices, so more and more citizens should be slaughtered to appease the gods.
Usually, this seemed to work, the drought ended, and the credibility of the priests was enhanced (just as sick people mostly get better, and in olden times this might be taken as proof that the medicine worked -- in the days before double-blind trials).
