Today we’re diving into one of the most colorful idioms in English: “let the cat out of the bag.” You’ll learn what it means, where it comes from, and how it’s used in real conversations.
We’re using a hilarious and dramatic scene from Sherlock to bring this lesson to life. Sherlock Holmes has faked his death—and now he’s revealing the truth to his best friend, John Watson. But why did he keep it a secret? Because he was afraid John might let the cat out of the bag.
👇 Watch the full lesson below, then scroll down for all the vocabulary and deeper explanations.
Letting the Cat out of the Bag with Sherlock
2. “Oh, brilliant(!)” – Sarcasm alert
3. “Right, no, no, this is charming. I’ve really missed this(!)”
1) Indiscreet (adj)
📖 Discreet means careful about what you say, so you don’t share secrets or cause problems.
💬 “She was very discreet about their breakup—she didn’t tell anyone the details.”
📖 Indiscreet is the opposite: careless or saying something at the wrong time.
💬 “It was indiscreet of him to talk about his boss’s mistakes in front of everyone.”
2) "Oh, brilliant(!)" – Sarcasm alert
📖 Normally, “brilliant” means smart, clever, or amazing.
But here, John uses it sarcastically. He’s not happy—he’s frustrated.
💬 “Oh, brilliant(!)” = “Great… I’ve been walking around with this moustache for no reason!”
The (!) in writing helps signal sarcasm—when someone says the opposite of what they actually mean.
3) "Right, no, no, this is charming. I’ve really missed this(!)"
📖 “Charming” usually means delightful or pleasant. But here, it’s sarcastic.
💬 John isn’t happy to see Sherlock criticizing him—he’s annoyed. That’s why he exaggerates with “really missed this(!)” to show he means the opposite.
💡 Tip: Sarcasm in English is all about tone. You’ll often hear exaggerated stress or a fake cheerful voice.
4) Waltz (in)
📖 This verb comes from the elegant ballroom dance, but it’s often used to describe someone walking in casually or confidently, sometimes when they shouldn’t.
💬 “After missing two weeks of work, he just waltzed in like nothing happened!”
💬 “She waltzed into my house without even knocking!”
It can imply arrogance, confidence, or simply not caring about the situation.
5) Large as bloody life
📖 A British phrase used when someone shows up in person unexpectedly or suddenly.
💬 “I thought she had moved abroad, and then I saw her in the park—large as life!”
“Bloody” is a common British slang word used for emphasis—it adds emotion, not literal meaning.
💬 “It’s bloody freezing today!” (very cold)
💬 “He’s bloody good at chess.” (very good)
💡 Note: “Bloody” is mild slang in the UK but not as common in American English.
6) Overreacting
To overreact means to respond too emotionally or make a big deal out of something small.
💬 “He said one small thing and she totally overreacted!”
“Over-” is a prefix meaning “too much.” Other examples:
- Overthink – “I overthink everything.”
- Overeat – “I overate and now I feel sick.”
- Overwork – “He’s been overworking for months.”
- Overspend – “I overspent on clothes this month.”
7) Swear to God!
📖 This phrase is used to strongly promise something is true.
💬 “I swear to God, I didn’t take your phone!”
People say this to show sincerity or to convince someone they’re not lying.
💡 Alternatives:
- “I swear on my life.”
- “I swear on my mother’s grave.”
Some people avoid “Swear to God” for religious reasons.
8) The thrill of the chase
📖 This expression means you enjoy the excitement of trying to get something, not just getting it.
💬 “He doesn’t want a relationship. He just enjoys the thrill of the chase.”
🧠 Originally used in hunting—it was the chase itself that excited people.
💬 “For some athletes, the thrill of the chase matters more than the trophy.”
“Thrill” = a rush of excitement
- “That rollercoaster gave me a thrill!”
- “He’s a thrill-seeker—always skydiving or bungee-jumping!”
9) Imminent
📖 “Imminent” means something is about to happen very soon, often something serious.
💬 “The storm is imminent—we need to find shelter!”
💬 “Her exam is imminent and she’s getting nervous.”
💡 Compare:
- “Dinner is soon.” → Calm, general.
- “An attack is imminent.” → Urgent, serious.
10) Idiom Spotlight | Let the Cat Out of the Bag" Mean?
▶️ Watch this quick YouTube Short to learn the full story behind the idiom:
📖 To let the cat out of the bag means to accidentally reveal a secret.
💬 “Don’t let the cat out of the bag—we’re throwing her a surprise party!”
Where does the idiom come from?
The most popular theory dates back to medieval markets. Farmers sold piglets in sacks called “pokes.” Dishonest sellers would sometimes swap the piglet for a cat and hope the buyer wouldn’t check the bag.
If the buyer opened it early, the cat would jump out, exposing the trick.
That’s why “letting the cat out of the bag” came to mean exposing a secret—often by accident.
📜 The first known use of the phrase was in 1760, in The London Magazine—proving it’s been around for over 250 years.
11) Bonus Tip: Idiom vs. Phrase
📖 A phrase is any group of words (e.g., “the red car”, “in the kitchen”).
📖 An idiom is a phrase with a hidden, non-literal meaning.
💬 “Let the cat out of the bag” doesn’t make sense literally—it’s not about cats or bags at all!
That’s what makes it an idiom.
Thanks for reading!
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