Graeae Eye
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The Myth
The Graeae shared one eye and one tooth between the three of them. In order to obtain information about where to find the objects he needed to kill Medusa (though some sources say he was looking for information on where to find Medusa herself), Perseus stole the eye as the sisters were passing it back and forth to each other and held it for ransom in exchange for that information.
In Young Hercules
In the series, the three sisters still shared the one eye. When they were trying to see Hercules, Iolaus, and Jason as the trio passed, the sisters began fighting over who would get to look next. As a result, they dropped the eye. Hercules picked it up and, with it, was granted the ability to see the future.