h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

In the 'Pig in a poke' definition you mention 'letting the cat out of the bag'

I was taught that was a Navy reference to the 'cat of nine tails' used for corporal punishment.

Although the sailors could be whipped for minor infractions every man was entitled to a 'clean cat in a fresh hand' meaning both the whip and the man swinging it had to be changed for each punishment. The whip was stored in a cloth bag to keep it clean. Before the flogging could begin the cat had to be taken out of its bag.

This why the phrase is often used to warn somebody not to tell a secret that could get themselves or others into trouble.

I found about half the slang mentioned is also common in the US, at least in the south east - still a fun read through

F S