How killing begets more killing (of bugs)

"At first killing was obligatory; afterward we got used to it. We became naturally cruel. We no longer needed encouragement or fines to kill, or even orders or advice."
Jean-Baptise Murangira, a killer from Rwanda.

There's plenty of anecdotal evidence that killing escalates - that the more a person kills, the easier they find it to kill again. A new study discussed on our Research Digest has looked at this idea experimentally, using a bug killing paradigm.