How does Ishi know what to do with Timawi's body after he finds him dead in the woods?

Ishi is not even aware that he is headed to Ancestor Cave until he falls and realizes that he has carried Timawi's body almost the whole way to the cave. He believes that his feet have taken him to the cave, guided by the Ancestor Spirits, so that he can properly bury Timawi. Once there, he follows all of the rituals that he had heard about in the stories from Elder Uncle and Grandfather. Having never seen the rituals performed, he relies on his memory and those stories.