Being treated fairly by others is an important social need. Experimentally, fairness can be studied using the Ultimatum Game in which the decision to reject a low, but non-zero, offer is seen as a way to punish the other player for an unacceptable division. The canonical explanation of such behavior is inequity aversion: people prefer equal outcomes over personal gains (Fehr, Schmidt, 1999). However, there is abundant evidence that the decision to reject a low offer can be changed by both contextual factors and emotional state, which cannot be satisfactorily explained by the inequity aversion model.