Ultimatum games have the following setup. Call one person the “offerer” and the other the “responder”, The offerer is informed that she can allocate a certain amount of a good. Suppose the good is money, such as $10, since that is the usual good chosen by experimenters in the literature. Next the offerer is instructed to make some offer to the responder—in our example, the offer could range between $0 and $10, inclusive. So the offerer can give away all the money, none of it, or something in-between. The only other piece of information that the offerer knows, standardly, is that the responder’s reaction matters when he is presented with her offer. If the responder accepts the offer, then both parties keep whatever the offer says (unless it is $0, in which case only one side keeps any money). But if the responder rejects the offer, then neither side gets any money at all, and the game is done. Hence if the offer is to keep $8 and give $2, and the responder accepts this offer, then that is in fact the amount of money with which each side walks away. But if the responder rejects the offer, then each side walks away with $0.