Pretty/fine kettle of fish avoid committing oneself to a course of action this meaning is an obvious development from an earlier and still current one: to proceed timidly, evasively or warily. Although this makes sense in terms of the gentleness and lightness of a cat's normal movement, it originates in an even earlier piece of american slang that had to do with sly behaviour, as of a cat creeping up on its prey - quite different from the current meaning.
And here's another experience!
Your stomach has to produce a new layer of mucus every 2 weeks otherwise it will digest itself.
