The Ultimatum game is an experimental economics game in which two parties interact anonymously and only once, so reciprocation is not an issue. The first player proposes how to divide a sum of money with the second party. If the second player rejects this division, neither gets anything. Classical economics suggests that the first player should offer only a small amount and the second should accept it. But, in many cultures, people (except economics grad students) offer "fair" (50:50) splits, and offers of <20% are often rejected.