In the legend of Vishnu's decapitation, the sacrifice is stated to have begun without the Ashvins. Wilkins relates another legend in the Shatapatha Brahmana (4.1.5) that leads to the Ashvins joining the sacrifice, and as physicians, using their power to replace the head of Vishnu/Makha as the head of the sacrifice (i.e. the Pravargya, itself). Their request to the gods for this was to be granted oblations at the sacrifice, which was accepted (hence boiled milk is offered to them in the Pravargya sacrifice). The story related by Wilkins is that after attempting and failing twice to take away Sukanya, the young wife of an elderly Rishi called Chyavana, she tells the Ashvins one of the reasons she won't leave her husband for them is because they are imperfect, but will only tell them why after they make her husband young again. They agree, and so she 'tells the Asvins that they are imperfect because they have not been invited to join the other gods in a great sacrifice that was to be celebrated at Kurukshetra [where Vishnu/Makha is later decapitated]. The Asvins proceed to this sacrifice, and, asking to be allowed to join in it, are told they cannot do so, because they have wandered familiarly among men, performing cures. In reply to this, the Asvins declared that the gods were making a headless sacrifice. The gods inquiring how this can be, the Asvins reply, Invite us to join you, and we will tell you. To this the gods consented'.