Understanding the prohibition of pesik reisheih as a form of davar she’ein mitkavein

Abstract

The phrase "running around like a headless chicken" is based on a somewhat bizarre scientific reality. When a chicken's head is cut off, the chicken can continue running around for several minutes, utterly headless. Significantly, this peculiar phenomenon of a headless chicken is also a critical concept in halakhah. Throughout Shas1, the phrase pesik reisheih vlo ymut is often posed as a rhetorical question meaning, “Is it possible to cut off the head and not die?” The case discussed is one in which someone severs the head of a chicken to use the head, but has no intention to kill the chicken. In this case, even though the chicken continues running around without a head for a few minutes, its imminent death is inevitable. Based on this case, the term pesik reisheih is employed to reference an unintended consequence that will definitely occur. More specifically, the term, pesik reisheih, is used in cases when the unintended consequence is a prohibited action. There is a clear consensus, in the Gemara, that pesik reisheih, an action with an unintended, prohibited consequence, is prohibited2. Understanding the logic qualifying this prohibition of pesik reisheih, however, is less clear.