Zoo Animals
Farm Animals
Cats and Dogs
Birds
Sea Creatures
100

Elephant in the room

Situation that everyone is aware of but no one wants to talk about

100

Hold your horses!

Wait a minute

100

Lucky dog

Lucky person

100

Watch like a hawk

Watch very closely

100

Fish out of water

Feeling out of place

200

Busy beaver

Someone who is very busy

200

Pig-headed

Stubborn

200

Cat got your tongue?

What you ask when someone is being quiet for no reason

200

Ducks in a row

Having everything organized

200

Something is fishy

Something is strange about a situation

300

Guinea pig

Test subject for something

300

You can lead a horse to water but you can't make it drink

You can prepare someone to do something but you can't make them do it

300

Let the cat out of the bag

Reveal a secret

300

The early bird gets the worm

The person who gets to a situation first is more likely to succeed

300

Big fish in a small pond

Someone who is important in a limited arena

400
A leopard can't change its spots

People don't often change

400

Don't look a gift horse in the mouth

Don't refuse an opportunity or a gift that someone gives you

400

Cat's meow

Something good

400

Night Owl

Someone who is more productive at night

400

Crocodile tears

Fake crying

500

Monkeying around

Fooling or joking around

500

Get Your Goat

Someone/something annoying 

500
You can't teach an old dog new tricks

It's difficult to add a new step to someone's routine 

500

Happy as a lark

Someone who is very happy

500

The world is your oyster

You can do anything you put your mind to