There were several ways in which Deino and her sisters Enys and Pemphredo were unique. First, they had been gray-haired since their birth (hence their name). But even more interesting, they only shared one eye and one tooth among them. This occasionally led to trouble.
In one mythological story King Polydectes sent Perseus off to bring back the head of Medusa, one of the Gorgons. Since Perseus needed information on where to find Medusa, he went to Deino and the other two Graeae. As the sisters were passing their eye between them, Perseus snatched it and held it until they told him everything he wanted to know.