In phase 1 of our experiment every participant plays the ultimatum game with each of the other five group members, each taking the role of proposer and responder. For each of the offers one learns how many participants would have accepted it. The pie is 30 times larger in phase 2. It thus pays to explore response behavior in phase 1 by choosing different offers in order to exploit responders in phase 2. Such experimentation is useless, however, if one wants to play fair, e.g. 50:50, or if one believes in the game theoretic solution. Sixty-one participants out of 77 (only those participants were included in the analysis who correctly answered the control question and whose responder strategy in phase 2 was monotonous) engaged in experimentation by submitting different offers in phase 1, whereas the remaining 16 participants submitted equal offers. Thirteen participants not engaged in experimentation divided equally, whereas the remaining 3 participants offered the smallest positive fraction of the pie.
