Young children will pay to watch a puppet being beaten, but only six-year-olds pay more to watch punishment inflicted on a puppet that personally offended them, according to scientists trying to figure out when our sense of fairness first develops.

In a beautifully macabre study published today in Nature Human Behaviour, 72 children aged four to six individually interacted with puppets in a miniature theater. One of the puppets gave the child a toy, while the other offered the toy and then withheld it. Next, a third puppet appeared onstage with a large stick and proceeded to beat whichever puppet was still onstage (this alternated based on the child) while it made crying sounds.

After a little while, the curtain fell and it was time to make a decision. The children indicated whether they wanted to continue watching by putting tokens to either the left or right of the stage. (The punishment would continue even if they didn’t watch.) If they did pay to witness the carnage, the curtain would fall again after a few seconds, and the punisher puppet would ask whether they wanted to keep paying to see more, for a total of four rounds.

Children of all ages paid to continue watching puppet punishment

Children of all ages paid to continue watching punishment, but only six-year-olds paid more to watch the mean puppet get punished. Also, only six-year-olds had more frequent smiles rather than frowns when they watched the mean puppet get punished.

The good news is that people of all ages seemed to be sad when the good puppet was being punished — and, to be fair to the younger kids, it’s possible they didn’t fully understand what was going on, as opposed to truly desiring vengeance on good puppets. In the grand scheme of things, six is fairly young to develop a sense of justice. Just be careful around the younger kids.