Leila relaxed exaggeratedly in her chair, her cheshire-cat smile predominating her features.
Alice was a little startled by seeing the cheshire-cat sitting on a bough of a tree a few yards off.
But on the cheshire-cat hypothesis, the social problem can never be solved, because it is not a real problem at all.
a cat with a broad grin, esp. fictitious
from Lewis Carroll's Alice's Adventures in Wonderland