The Cheshire Cat's grin is an expression originating from Lewis Carroll's fairy tale novel «Alice's Adventures in Wonderland» (1865). In the book, the Cheshire Cat is a mysterious creature capable of appearing and vanishing piece by piece, leaving behind, last of all, only a wide grin hanging in midair.
In modern culture, a «Cheshire Cat grin» means a wide, mysterious, often sly or knowing smile that lingers longer than usual and hints that the person smiling knows more than they're letting on.
The image of the Cheshire Cat has become one of the most recognizable characters in world literature. His catchphrase «We're all mad here — both you and I» captures the absurdity and whimsical logic of Wonderland.
There are several theories about the origin of the phrase «Cheshire cat»: one links it to cat-shaped cheeses once produced in the county of Cheshire; another to the heraldic lions on local noble family crests, depicted baring their teeth in a way that resembled a grin.
In film adaptations and illustrations, the Cheshire Cat is usually shown with an enormous, crescent-shaped grin baring all its teeth, often with a sly, narrowed gaze.