Who stole the office stapler? A study in April's Psychological Science argues it's more likely to have been your happiest colleague than your grumpiest. Observing that happier people are more mentally flexible, psychologists at Cornell University wondered whether they might be more morally flexible as well. To find out, the team showed 90 undergraduates either a cheerful video of a cartoon duck showering or a neutral screensaver. In addition, half of each group sat in front of mirrors to promote self-awareness. Finally, participants worked on 20 puzzles, earning 50 cents for each correct solution, with a sneaky bonus: because they scored themselves, they could get away with taking more than they'd earned. The happier, less self-aware group—those who'd watched the cartoon without a mirror—stole $1.17 on average, more than twice what any other group took. Further analysis suggested that these participants were also less morally engaged, which may explain their thievery.