In De Anima B6, Aristotle divides objects of perception into essential and incidental ones. Furthermore, he divides objects of incidental perception into three kinds. (1) common objects, (2) proper objects of heterogeneous perception, and (3) objects such as "son of Diares". Many Commentators think that the latter two are irrelevant to Aristotle's theory of perception. I think, however, these kinds of perception play the most important part not only in recognizing the existence of individual objects, but also explaining animal behaviors. By analyzing De Anima B6 and Γ1, I propose three levels of incidental perception: 1) Five proper senses perceive incidentally common objects. 2) Each proper sense perceives incidentally objects of proper senses other than itself. 3) Common sense and proper senses perceive incidentally objects such as "son of Diares".