The Hardest Tongue Twister in the World

Every list of tough phrases eventually gets asked the same question: what’s the actual hardest tongue twister in the world? Not the hardest for you personally, or the hardest one your teacher knows — the hardest one that’s ever been tested, measured, and confirmed to trip people up more than any other. It turns out researchers have actually studied this question in a lab, and the answer might surprise you.

This page breaks down the scientifically-tested answer, the classic contender that held the title before it, why both of them are so difficult to say, and how to actually practice them if you want to try.

What Makes a Tongue Twister the Hardest?

Most tongue twisters trip you up because they repeat similar sounds in a way that confuses the brain’s speech-planning process. But not all twisters are equally hard. The truly difficult ones share a specific pattern: they alternate between two or more similar consonant sounds at the start of consecutive words, rather than just repeating the same sound over and over. This “alternating repetition” forces your brain to constantly switch instructions for your tongue and lips mid-sentence, which is a much harder task than repeating one sound in a row.

The Lab-Tested Hardest Tongue Twister: “Pad Kid Poured Curd Pulled Cod”

In 2013, a team of researchers at MIT, led by psychologist Stefanie Shattuck-Hufnagel, set out to study speech errors by deliberately constructing the most difficult tongue twister they could design. The result, “pad kid poured curd pulled cod,” was so effective that many test subjects couldn’t complete it at all, and some simply gave up mid-attempt.

Shattuck-Hufnagel reportedly told participants, “if anyone can say this ten times quickly, they get a prize” — and by most accounts, no one claimed it. The phrase was presented at the Acoustical Society of America’s annual meeting alongside research comparing two types of tongue twisters: simple repeated word pairs like “top cop,” and full sentence versions of the same sound patterns. Both types produced speech errors, which suggested to researchers that the same underlying brain process handles both word-level and sentence-level speech planning.

What makes this particular phrase so brutal is that it has no real meaning to lean on. Ordinary tongue twisters like “she sells seashells” at least form a coherent sentence your brain can predict as you go. “Pad kid poured curd pulled cod” reads as nonsense, so your brain gets no contextual help guessing what comes next — it has to process each jarring consonant switch in real time, with nothing to fall back on.

The Classic Contender: “The Sixth Sick Sheik’s Sixth Sheep’s Sick”

Before MIT’s 2013 research, the title of hardest tongue twister in the world was widely credited to a different phrase: “the sixth sick sheik’s sixth sheep’s sick.” This sentence has been cited by language reference sources like the Guinness Book of World Records and by word expert William Poundstone, who in 1990 named it the toughest tongue twister he knew of.

Its difficulty comes from a dense cluster of /s/, /sh/, and /th/ sounds packed into just eight words, forcing your tongue to shift position for nearly every syllable. Unlike the MIT phrase, it does form an actual (if odd) sentence, which arguably makes it slightly easier — your brain can at least follow the grammar, even while your tongue struggles with the sounds.

Other Twisters Often Called “The Hardest”

A few other phrases show up regularly in “hardest tongue twister” discussions, even though they haven’t been tested in a lab the way the MIT phrase was:

• “The seething sea ceaseth and thus the seething sea sufficeth us” — Poundstone’s runner-up, built on repeated /s/ and /th/ sounds.
• “Toy boat” — deceptively short, but almost impossible to repeat quickly more than a few times without it collapsing into “toy boyt.”
• “Red lorry, yellow lorry” — a favorite among voice coaches for how consistently it turns into “yellow lolly.”

None of these have been shown to be harder than the MIT phrase in controlled testing, but they’re worth trying if you want to feel the same kind of speech breakdown on a smaller scale.

Why Even Native Speakers Fail

It’s not just ESL learners who stumble on these phrases — native English speakers fail them constantly, which is exactly what makes them useful research tools. When two similar sounds sit close together in a sentence, your brain has to send extremely precise, fast-changing instructions to your tongue, lips, and jaw. Under time pressure, those instructions can arrive slightly out of order, or blend together, producing the classic tongue-twister slip. Researchers found two distinct error patterns depending on whether the sounds were arranged as a simple word list or a full sentence, which suggests your brain plans short phrases and full sentences slightly differently, even though both can break down the same way.

How to Practice the Hardest Tongue Twister Yourself

• Start syllable by syllable. Break “pad kid poured curd pulled cod” into individual words before trying to connect them.
• Say it slowly at first. Speed is the last step, not the first — accuracy has to come before you push the pace.
• Record yourself. These phrases fail in very specific, repeatable ways, so listening back will show you exactly where your tongue is losing control.
• Don’t expect to “win.” Even the MIT researchers who designed it struggled to say it ten times quickly — the goal is progress, not perfection.
• Warm up with easier twisters first if you’re newer to English pronunciation practice, rather than starting here.

Frequently Asked Questions

What is the hardest tongue twister in the world?

Based on controlled research, “pad kid poured curd pulled cod,” designed by MIT researchers in 2013, is widely considered the hardest tongue twister in the world, since it caused more speech errors in testing than any other phrase studied.

Is “the sixth sick sheik’s sixth sheep’s sick” the hardest tongue twister?

It was considered the hardest tongue twister before MIT’s 2013 research, and it’s still one of the toughest ones with an actual sentence structure, rather than nonsense wording.

Why is “pad kid poured curd pulled cod” so hard to say?

It alternates between similar consonant sounds at the start of each word, and it doesn’t form a meaningful sentence, so your brain has no context to help predict what comes next as you speak.

What to Read Next

Ready for more, or want to build up to this one gradually? Here’s where to go next:

• 50 Easy & Short Tongue Twisters for Beginners — if you want to build up gradually first.
• 100 Hard English Tongue Twisters for Perfect Pronunciation — for more of a challenge before you attempt this one.
• The Complete Guide to English Tongue Twisters — for the full picture.