This is a video about human computation. At one point the speaker is talking about the ESP game a game google made that lets people play to label images in there image search, you have to try and type the same word as the other person and if you both type the same word you both get a point. Adding a simple message that said your partner has entered a name kept people playing for 4% longer, it shows how such a little thing can make people enjoy your game more and make them want to play for longer.