the cat's pajamas

cat's cradle

Any complicated structure that appears to be without purpose.

cat's meow

A self-satisfied person.

look what the cat's dragged in

Used as an ironic acknowledgement of someone's arrival, either jocularly or to imply that they are unwelcome or disagreeable in some way.

the cat's out of the bag

It is too late. Particularly used of secrets that have been exposed.

the cat's pyjamas

A highly sought-after and fancy example of something, usually referring to inanimate objects.

who's 'she', the cat's mother

A rebuke especially directed towards children for having referred to a woman in the nominative case as "she", instead of by her name or an appropriately respectful title.