The researchers asked 156 participants to write an essay on a personal topic, then to swap their essays with other participants to receive feedback on what they’d written. One group of participants received nasty feedback (actually composed by the researchers): “one of the worst essays I have EVER read”. Chester and DeWall measured mood before and after participants were given the chance to express a symbolic form of aggression: sticking pins in a virtual voodoo doll imagined as the person who had given them mean feedback. This act of (un)sympathetic magic did indeed repair mood for the rejected participants, to the point where their mood was indistinguishable from participants who’d received nice feedback.

But just because revenge can boost our mood doesn’t mean that we behave aggressively because we’re seeking that better mood. To investigate motives, the researchers next invited 154 participants to the lab and gave each a pill, telling them it would enhance their thinking for the tests to come. Some of the participants were further told that the pill had a peculiar side-effect: once it kicked in, their mood would become fixed and unchanging (all these claims about the pill were a fiction, it was an inert placebo).