An idiom is a fixed expression whose meaning can't be worked out from the individual words. "Let the cat out of the bag" has nothing to do with cats — it means revealing a secret. Animal idioms are especially common because they use familiar images: a stubborn mule, a loyal dog, a sly fox.
Cat idioms
| Idiom | Meaning | Example |
|---|---|---|
| let the cat out of the bag | reveal a secret by accident | We planned a surprise party, but Ravi let the cat out of the bag. |
| like a cat on hot bricks (UK) | very nervous and unable to keep still | She was like a cat on hot bricks waiting for her results. |
| a copycat | someone who copies others | Don't be a copycat — write your own answer. |
| the cat's whiskers / the cat's pyjamas (old-fashioned) | excellent, the best | He thinks his new phone is the cat's whiskers. |
Dog idioms
| Idiom | Meaning | Example |
|---|---|---|
| raining cats and dogs | raining very heavily | Take an umbrella — it's raining cats and dogs. |
| in the doghouse | in trouble with someone | He forgot their anniversary, so he's in the doghouse. |
| let sleeping dogs lie | don't restart an old problem | They've stopped arguing about it — let sleeping dogs lie. |
| barking up the wrong tree | blaming or asking the wrong person; looking in the wrong place | If you think I took your charger, you're barking up the wrong tree. |
| a dog-eat-dog world | a fiercely competitive situation | Startup funding is a dog-eat-dog world. |
Horse idioms
| Idiom | Meaning | Example |
|---|---|---|
| hold your horses | wait; slow down | Hold your horses — let's read the instructions first. |
| straight from the horse's mouth | directly from the person who knows | The exam is postponed — I heard it straight from the horse's mouth: the principal. |
| a dark horse | someone with hidden talents who succeeds unexpectedly | Nobody expected Meera to win the debate — she's a dark horse. |
| put the cart before the horse | do things in the wrong order | Designing the logo before deciding the business idea is putting the cart before the horse. |
Bird idioms
| Idiom | Meaning | Example |
|---|---|---|
| kill two birds with one stone | achieve two things with one action | Walking to work kills two birds with one stone: exercise and no traffic. |
| a little bird told me | I heard it from someone (I won't say who) | A little bird told me you got promoted! |
| a wild goose chase | a hopeless search for something you won't find | Looking for that old receipt was a wild goose chase. |
| as the crow flies | in a straight line (distance) | The station is 2 km away as the crow flies, but 4 km by road. |
Elephants, bulls, cows and other animals
| Idiom | Meaning | Example |
|---|---|---|
| the elephant in the room | an obvious problem nobody wants to mention | The budget cut was the elephant in the room at the meeting. |
| a white elephant | an expensive possession that is useless or costly to maintain | The huge stadium became a white elephant after the games ended. |
| like a bull in a china shop | clumsy or tactless in a delicate situation | He handled the complaint like a bull in a china shop. |
| until the cows come home | for a very long time (often uselessly) | You can argue until the cows come home — I won't change my mind. |
| crocodile tears | fake sadness | He cried crocodile tears after breaking the vase on purpose. |
| the lion's share | the largest part | Rent takes the lion's share of my salary. |
| a fish out of water | uncomfortable in an unfamiliar situation | On my first day at the new office, I felt like a fish out of water. |
| the black sheep (of the family) | the member who is different or seen as a disappointment | He was the black sheep of the family until his business succeeded. |
| open a can of worms | start something that creates many new problems | Asking about salaries in the meeting opened a can of worms. |
| when pigs fly | never; it will never happen | He'll clean his room when pigs fly. |
| have butterflies in your stomach | feel nervous before something | I always have butterflies in my stomach before an interview. |
| as stubborn as a mule | extremely stubborn | My grandfather is as stubborn as a mule about his diet. |
Where do animal idioms come from?
Many come from farming and everyday rural life, when animals were part of daily work. Put the cart before the horse is a straightforward farming image. Crocodile tears comes from an old belief that crocodiles weep while eating their prey. A white elephant is linked to stories of rare white elephants in South-East Asia, which were sacred, could not be put to work, and were costly to keep. Origins of idioms are often uncertain, so treat colourful origin stories as interesting rather than proven.
Using animal idioms well
- Keep the exact words. "Let the dog out of the bag" or "raining cats and cows" sounds wrong — idioms are fixed.
- Match the tone. Most of these are informal. In an IELTS essay or formal email, use plain words: "an obvious problem" instead of "the elephant in the room".
- Don't overdo it. One idiom in a conversation sounds natural; five in a paragraph sounds forced.
- Watch grammar inside the idiom. She let (past) the cat out of the bag; You're barking (continuous) up the wrong tree.
Quick quiz: complete the idiom.
- The new mall is a white ______ — it's always empty.
- Don't tell anyone — I don't want you to let the ______ out of the bag.
- We searched every shop, but it was a wild ______ chase.
- Nobody wanted to talk about the ______ in the room: the delay.
- Hold your ______! We haven't decided anything yet.
- I'll believe he's on time when ______ fly.
Show answers
- elephant
- cat
- goose
- elephant
- horses
- pigs
Next, try idioms built on another everyday image — the human body — in body idioms, or learn how idioms differ from English proverbs.
Frequently asked questions
What are animal idioms?
Animal idioms are fixed English expressions that mention an animal but have a figurative meaning, such as “let the cat out of the bag” (reveal a secret) or “the elephant in the room” (an obvious problem nobody mentions).
What does “raining cats and dogs” mean?
It means raining very heavily. It is informal and common in both British and American English.
What does “a dark horse” mean?
A dark horse is a person who has hidden abilities and surprises others by succeeding, often in a competition.
Can I use animal idioms in an essay?
Usually not in formal or exam essays, because most idioms are informal. Use them in conversation, informal emails and creative writing instead.
What is the difference between an idiom and a proverb?
An idiom is a phrase with a figurative meaning that fits into a sentence (“hold your horses”). A proverb is a complete saying that gives advice or a general truth (“Don’t count your chickens before they hatch”).