Plutarch devotes two essays to the familiar theme of the craftiness and sagacity of animals and the remedies used by them. In one essay[985] a companion of Odysseus refuses to allow Circe to turn him back from a pig to human form. He boasts among other things that beasts know how to cure themselves. Without ever having been taught swine when sick run to rivers to search for craw-fish; tortoises physic themselves with origanum after eating vipers; and Cretan goats devour dittany to extract arrows and darts which have been shot into their bodies. In the other essay[986] on the cleverness of animals we find many familiar stories repeated, including some of the inevitable excerpts from Juba on elephants. We meet again the dolphins with their love for mankind,[987] the bird who picks the crocodile’s teeth and warns him of the ichneumon,[988] the fish who rescue one another by biting the line or dragging one another by the tail out of nets,[989] the trained elephant who was slow to learn and was beaten for it and was afterwards seen practicing his exercises by himself in the moonlight,[990] the sentinel cranes who stand on one foot and hold a stone in the other to awaken them if they let it drop.[991] More novel perhaps is the story how herons open oysters by first swallowing them, shells and all, until they are relaxed by the internal heat of the bird, which then vomits them up and eats them out of the shells. Or the account of the tunny fish who needs no astrological canons and is familiar with arithmetic, “Yes, by Zeus, and with optics, too.”[992] [Sidenote: Theories and queries about nature.]