Scientists convince their friends to get punched in the arm by robots... for science.
I'm assigning this article to my intro modeling class to try and get them thinking about AI representations. A robot doesn't know what "pain" is, so you can't just tell it "don't cause pain." Instead, you have to operationalize "pain": that's what this study is trying to do by saying "look, it is bad if you move at X speed when you are grasping Y implement." Then, when the robot detects a human nearby (a whole nother gigantic, difficult AI problem), it can know not to move faster than X.