A book for people who've mastered such basics as a pride of lions and want to go onward. To a murder of crows, a parliament of owls, or a truelove of doves.
You can have your pick for cats: clowder, cluster, and clutter are all recorded. Though some have distinctions: it is a gaggle of geese on the grounds, but a skein of geese in the air.
Some are more fun than others, and he includes a long section with possibilities for new ones.