The Cheshire cat is a fictional character that appears in Lewis Carroll’s Alice’s Adventures in Wonderland (1865). It is able to disappear and reappear at will, and even to disappear in sections; at one point Alice is left with only the cat’s smile. When Alice asks the cat’s owner, the Duchess, “Please, would you tell me why your cat grins like that?” she is told that it is a Cheshire cat, as if that explains everything.
The poet T. S. Eliot may have had the Cheshire cat in mind when writing the last two lines of “Morning at the Window”:
An aimless smile that hovers in the air
And vanishes along the level of the roofs.
The phrase “to grin like a Cheshire cat” predates Alice’s Adventures in Wonderland; one of the earliest recorded uses of the phrase appears in John Wolcot’s Works, (1812). It was well known in Carroll’s time, but its origin is obscure.
One suggestion is that a signwriter in Cheshire painted smiling lions on the signboards of inns in the area. Another is that Cheshire cheeses were at one time moulded in the shape of a grinning cat. Yet another suggestion is that it may derive from the waning of the Moon, when it turns into a smile-shaped crescent before disappearing.
The Cheshire Cat effect is the name given to a form of binocular rivalry in which a moving object seen by one eye renders invisible a stationary object in the same region of the visual field of the other eye. The same name has been given to a quantum mechanical effect in which the property of a particle, such as its spin, can be separated from its position.