One of the major clues that elephants have something we would recognize as inner lives is their extraordinary memories. This is attested to by outward indicators ranging from the practical — a matriarch’s recollection of a locale, critical to leading her family to food and water — to the passionate — grudges that are held against specific people or types of people for decades or even generations, or fierce affection for a long-lost friend.
http://www.thenewatlantis.com/publications/do-elephants-have-souls