Why do some people take pleasure in cruelty?

If you had the opportunity to feed harmless bugs into a coffee grinder, would you enjoy the experience? Even if the bugs had names, and you could hear their shells painfully crunching?
 And would you take a perverse pleasure from blasting an innocent bystander with an excruciating noise?
 These are just some of the tests that Delroy Paulhus uses to understand the “dark personalities” around us.