Whispered Secrets can be converted into a smaller number of Cryptic Clues, Cryptic Clues can be converted into a smaller number of Appalling Secrets. It's a better trade than selling Whispered Secrets to buy Clues would be, but worse if you just want to sell the Clues for money anyway. Appalling Secrets can be sacrificed in large numbers to reduce Nightmares, or turned into some kind of book item that I'm not sure of. Greyfields First Sporing can be drunk, reducing Nightmares by a fair bit.