[eesmith]

Several others have mentioned Martin Gardner's book "Annotated Alice". It has a section on the Cheshire cat's grin, at https://archive.org/details/agt-annotated-alice-5807b6/page/...

> "Grin like a Cheshire cat" was a common phrase in Carroll's day. Its origin is not known. The two leading theories are: (1) A sign painter in Cheshire (the county, by the way, where Carroll was born) painted grinning lions on the signboards of inns in the area (see Notes and Queries, No. 130, April 24, 1852, page 402); (2) Cheshire cheeses were at one time molded in the shape of a grinning cat (see Notes and Queries, No. 55, Nov. 16, 1850, page 412). "This has a peculiar Carrollian appeal," writes Dr. Phyllis Greenaere in her psychoanalytic study of Carroll, "as it provokes the fantasy that the cheesy cat may eat the rat that would eat the cheese." The Cheshire Cat is not in the original manuscript, Alice's Adventures Under Ground.

It continues with a full page on the topic, none of which are anything to do with math jokes.