Book excerpt: In 1955, armed with a penknife and instructions to keep the river on his right, Brooklyn-born artist Tobias Schneebaum set off into the jungles of Peru in search of a tribe of cannibals. Forgoing all contact with civilization, he lived as a brother with the Akaramas -- shaving and painting his body, hunting with Stone Age weapons, sleeping in the warmth of the body-pile.