If man could be crossed with the cat it would improve man, but it would deteriorate the cat.

The line comes from an 1894 entry in Twain’s personal notebooks. It was later published posthumously in a 1935 edited volume of his notebook excerpts prepared by his biographer and literary executor, Albert Bigelow Paine.

Twain is jokingly elevating cats above humans in terms of independence and resistance to coercion. The imagined crossbreeding is a humorous way to say people could benefit from feline traits, while cats would be diminished by acquiring human flaws.

Of all God’s creatures there is only one that cannot be made the slave of the lash. That one is the cat. If man could be crossed with the cat it would improve man, but it would deteriorate the cat.