Professor Ian Ayres of Yale Law School examines Kass v. Kass, a case about a couple's dispute over frozen embryos after divorce, as part of his American Contract Law course on formation defenses. The case turns on whether a prior agreement between the couple about disposition of the embryos should be enforced as a contract, and Ayres uses it to test the limits of promissory liability when the subject matter involves reproductive material rather than ordinary goods or services. He walks through the court's reasoning on informed consent, changed circumstances, and whether public policy should override a signed agreement. The lecture is one segment in a sequence on illegality and other formation defenses within the broader Coursera-based course, originally developed for Yale's American Contract Law I and II.