Hehh-duHpp was a Klingon exercise used to teach infants hand-eye coordination so they could grow up to become warriors. It involved shaking a rattle in front of them to teach them rhythm and hand-eye coordination.
While taking care of an infant Kirayoshi O'Brien in 2374, Worf tried to teach him some hehh-duHpp. Later, he was inordinately pleased to hear from his wife, Jadzia Dax, that Yoshi had been repeating the ritual phrase to himself. (DS9: "Time's Orphan")