1. Let the cat out of the bag

Meaning: To disclose a secret, normally without meaning to.

Origin: Paul Anthony Jones explains how the phrase originates from the days when you would go down to an agricultural fair and buy “a prize piglet that would get put in a sack and you’d take it back home and when you open the sack again you’d find it was just a stray cat, and you’d been had.”

Example: “The gift for my Mum was meant to be a surprise but Dad let the cat out of the bag by pointing out the parcel in the post.”

2. Don’t look a gift horse in the mouth

Meaning: Don't find fault with something that you’ve been given as a gift.

Origin: A horse’s value is determined by its age, and this can be worked out by looking in its mouth: a horse’s teeth get longer as it gets older. To look a horse you’ve been given in the mouth is therefore to assess its value and, quite frankly, on the rude side. This proverb first appeared in print in 1546 when John Heywood wrote: “No man ought to look a geuen [given] hors [horse] in the mouth.”

Example: “Thanks for my birthday present! Of course I’d rather the jumper wasn’t yellow, but I won’t look a gift horse in the mouth.”

3. The whole nine yards

Meaning: Everything there is, or all the way.

Origin: This is an idiom, Paul says, where “there are plenty of ideas” about its origins. Could it be the amount of fabric needed to make a kilt or a nun’s habit? The length of a WWII fighter pilot’s ammunition? The length of the hangman’s noose?