The article explores the question of pain in Aristotle’s philosophy and the way animals experience pain. Pain and its opposite pleasure play an important role in Aristotle’s ethics. This is mainly because of the close connection between pleasure and actuality (energeia). Aristotle argues that pleasure perfects the actuality as a supervenient perfection. The article tries to show that in order to understand the notion of pain in Aristotle, we must also comprehend the relation between pain and energeia. Even though some pains can be classified as kineseis, moving the animal out of his natural state, the article argues that pain can also be understood as distorting the energeia. Whereas pleasure perfects the energeia, pain hiders its perfection. The article shows what this notion of pain as hindrance means for animal life and how it relates to some other important areas of Aristotle’s philosophy, such as sense-perception and psychology. Thanks to his broad theory of the soul, Aristotle can explain pain in both animals and human beings and provide a theory for both bodily and psychical pain. Finally, the article argues that exploring Aristotle’s notion of pain can contribute not only to a better understanding of the notion of pain generally but also of some intricate parts of Aristotle’s philosophy, especially his theory of energeia.