1. Aesop, The Aesop for Children, Illustration by Milo Winter, Project Gutenberg etext 19994, http://www.gutenberg.org/etext/19994.
2. Rooks use stones to raise the water level to reach a floating worm;Bird;Curr. Biol.,2009
3. Causal knowledge in animals;Kummer,1995
4. Learning and Instinct in Animals;Thorpe,1964
5. Kinds of Minds: Toward an Understanding of Consciousness;Dennett,1996