A cat with an enormous grin encountered by Alice in Alice's Adventures in Wonderland, by Lewis Carroll. The cat tends to disappear, leaving only its smile hanging in the air.
grin like a Cheshire cat
Smile broadly, especially in a self-satisfied way. For example, John ended the set with a beautiful serve, an ace, and couldn't help grinning like a Cheshire cat. The ultimate origin of this expression, appearing in print since the late 1700s, is disputed, but its most famous exponent was Lewis Carroll, in whose Alice's Adventures in Wonderland the grinning cat gradually vanished from view, with its grin the last part to vanish.