Animals
Busy as a bee
Very busy and active
Piece of cake
Time is money
Time is valuable, so don't waste it
In the nick of time
At the last possible moment
Break someone's heart
To make someone very sad
The elephant in the room
An obvious problem that people avoid talking about
Spill the beans
To reveal a secret
On the house
Free of charge
Under the weather
Feeling sick or unwell
Cold feet
To suddenly feel nervous and afraid to do something
Let the cat out of the bag
Accidentally reveal a secret
Cool as a cucumber
Very calm, not nervous
Hit the jackpot
To have a lot of luck or success
A storm in a teacup
A big fuss about something small
Butterflies in my stomach
A nervous feeling in your stomach
A wild goose chase
A pointless or hopeless search
In a pickle
In a difficult or troublesome situation
Burning the midnight oil
Working late into the night
Once in a blue moon
Something very rare
See eye to eye
To agree with someone
Kill two birds with one stone
To accomplish two things at once
Salt of the earth
A very good, kind and honest person
To foot the bill
To pay the cost of something, often for others
Beat the clock
To finish something before the deadline/before time runs out
To wear your heart on your sleeve
To openly show your emotions