Getting a vaccine can be a painful experience, especially when you're a kid. But getting told the shot might "hurt a bit" could actually make it worse. "We know that expectation affects pain experience in adults. But we don't really know whether this is also true for children." Kalina Michalska, a developmental neuroscientist at the University of California, Riverside. She led a study to find out. The study included 25 adults and 48 children. And 27 of the kids had a pre-existing anxiety disorder. Because medical procedures make pretty much all kids anxious... and those who are anxious to start with tend to find the experience even more painful. The researchers used a handheld wand to apply heat to the forearm of each participant. And they asked subjects to rate the temperature in terms of discomfort. "But during the experiment, we were most interested in only one temperature: the one that each subject rated as medium."