Scáthach teaches Cú Chulainn all the arts of war, including the use of the Gáe Bulg, a terrible barbed spear, thrown with the foot, that has to be cut out of its victim. His fellow trainees include Ferdiad, who becomes Cú Chulainn's best friend and foster-brother. During his time there, Scáthach faces a battle against Aífe, her rival and in some versions her twin sister. Scáthach, knowing Aífe's prowess, fears for Cú Chulainn's life and gives him a powerful sleeping potion to keep him from the battle. However, because of Cú Chulainn's great strength, it only puts him to sleep for an hour, and he soon joins the fray. He fights Aífe in single combat, and the two are evenly matched, but Cú Chulainn distracts her by calling out that Aífe's horses and chariot, the things she values most in the world, have fallen off a cliff, and seizes her. He spares her life on the condition that she call off her enmity with Scáthach, and bear him a son.