From Roger Zelazny’s Trumps of Doom:
On the blue-gray ledge above me was crouched a sphinx, also blue — lion body, large feathered wings folded tight against it, a genderless face looking down upon me. It licked its lips and revealed a set of formidable teeth.
Get on with what?“ I asked, raising myself slowly into a sitting position and drawing several deep breaths.
“The riddling,” it answered, “the thing I do best.”
“I’ll take a rain check,” I said, waiting for the cramps in my arms and legs to pass.
“Sorry. I must insist.”
I rubbed my punctured forearm and glared at the creature. Most of the stories I recalled about sphinxes involved their devouring people who couldn’t answer riddles. I shook my head.
“I won’t play your game,” I said.
“In that case, you lose by forfeit,” it replied, shoulder muscles beginning to tighten.
From J. R. R. Tolkein’s The Hobbit:
“Sssss,” said Gollum, and became quite polite. “Praps ye sits here and chats with it a bitsy, my preciousss. It likes riddles, praps it does, does it?” He was anxious to appear friendly, at any rate for the moment, and until he found out more about the sword and the hobbit, whether he was quite alone really, whether he was good to eat, and whether Gollum was really hungry. Riddles were all he could think of. Asking them, and sometimes guessing them, had been the only game he had ever played with other funny creatures sitting in their holes in the long, long ago, before he lost all his friends and was driven away, alone, and crept down, down, into the dark under the mountains.
“Very well,” said Bilbo, who was anxious to agree, until he found out more about the creature, whether he was quite alone, whether he was fierce or hungry, and whether he was a friend of the goblins.
(My actual riddles have been taken down for now, but one day return…)