A certain spouse of our acquaintance has what we can only assume are religious objections to walking over to a wastepaper basket and dropping in his used Kleenex, crumpled envelope or other trash. Instead, he shoots what amount to living-room foul shots—occasionally hitting someone between him and the basket. This spouse has also been known—rarely!—to throw crumpled paper in anger,intentionally hitting someone. Question: why does it hurt more when he tries to hit you than when he hits you unintentionally? Related question: why does it hurt more if someone purposely stomps on your foot than if she accidentally treads on your toes?

Now Kurt Gray and Daniel M. Wegner of Harvard University have shown it’s not your imagination, or a case of hurt feelings being confused with a physical harm. As they write about “the sting of intentional pain” in the December issue of the journal Psychological Science, “the physical parameters of the harm may not differ—your toe is flattened in both cases,” but the intentional infliction of pain is, well, more painful.

Psychologists have known for years that pain has a strong mental component. The placebo effect (being given a sugar pill or other dummy treatment that a respected authority assures will help you) is especially potent at reducing pain, and the nocebo effect (being told you are about to feel something painful, even though nothing physical is actually administered) can cause pain: when told that a (nonexistent) electric current is passing through their heads, people say they get headaches, as a fascinating 1981 paper found.

For their study, the Harvard scientists paired 43 volunteers with partners (actually, one of the research assistants). The partner, they were told, would decide whether the volunteer would receive an electric shock or not. Sometimes, however, the experimental set-up would deliver a shock even when the partner had called for something else, the volunteers were told. The volunteer could see what the partner had called for and what was actually going to happen. That is, they could tell if the partnermeant to cause the volunteer to feel an electric shock (intentional) or if the shock occurred because of a mix-up (unintentional).

On a scale from 1 to 7, intended pain hurt 3.62 worth. An identical shock, which the volunteers thought was unintentional, hurt 3.00 worth.

Why? One clue comes from the finding that, in the brain, feelings of physical pain and social harm (such as being rejected) are processed by similar regions, as a 2003 study found. Social harms are, typically, intentional, and are more painful to relive than physical harms. If you combine physical pain (electric shock—or getting hit with a wadded-up Kleenex) with social pain (he meant to hit me!), the combination is that much more hurtful.

So if she tries to tell you that that little intentional stomp she gave your foot can't have hurt, or if he insists that a little bop on the head from the paper he hurled at you cannot have been painful, tell them science says otherwise.