Forget Peter and his peppers, and Sally and her seashells. Researchers at MIT claim they have found the twistiest tongue twister in the English language: "Pad kid poured curd pulled cod."

Presenting the work at the Acoustical Society of America in San Francisco last week, Stefanie Shattuck-Hufnagel, an MIT psychologist who helped coin the phrase, says it's so tricky that when she asked subjects to say it ten times fast, some became so tongue-tied that they simply gave up.

This puts it in the league of famously frustrating phrases like "Clean clams crammed in clean cans"; "The top cop saw a cop top"; and "The seething sea ceaseth and thus the seething sea sufficeth us."

So what makes some phrases harder to say than others? Researchers say tongue twisters share certain qualities that the human brain and mouth tend to reject. For example, they often contain a quick string of similar but distinct phonemes, which are the smallest linguistic unit (like "s" or "sh"). Inversions, such as "the top cop saw a cop top," also prove tricky. And "Pad kid poured curd pulled cod" has the extra bonus of being totally nonsensical.

Researchers have also identified the kinds of mistakes people tend to make when attempting these phrases. They often conflate consonants, a mistake linguists refer to as double onsets. "Top cop" sometimes becomes "tkop," for example. People also tend to turn vowels into mush. "Toy boat" very quickly becomes "tuh-boyt."

Is the brain jumbling the syllables, or are the muscles in our mouths unable to handle certain rapid movements? In 1982, researchers Ralph and Lyn Haber examined where the mistakes occur. Asking college-age test subjects to silently read two types of sentences — ones that contained tongue twisters, and ones that were similar in complexity, but did not contain tongue twisters — the Habers found that subjects slowed down on sentences with tongue twisters, even when their actual tongues were not in use. This implied that the brain is confusing the sounds before they ever reach the mouth.

How Stuff Works explains:

The findings indicate that phonology — the rhythmic patterns we assign to speech that include things like stress and inflection — plays a major role not only in the way we say words, but also how we process them while reading. When we read, one of the ways we sort them into comprehensible packages is by the arrangement of the sounds, or phonemes. In "toy boat" the /t/ sound is a phoneme, so is the /oy/, /b/ and long /o/. [How Stuff Works]

Then earlier this year, another set of researchers from University of California, San Francisco took a closer, more invasive look at the phenomenon. The scientists surgically implanted electrodes under the skulls of three epilepsy patients (a routine procedure), which allowed them to record electrical activity in the brain.

Patients then read from a list of English syllables, while researchers recorded the electrical response in their brains. What they found: The neural patterns that lit up when subjects articulated consonants were quite different from those of vowels, even though the parts of speech "use the exact same parts of the vocal tract," the study's author, Edward Chang, told Nature.

This helps explain why it's easier for the brain to confuse consonants and flip vowels with their own kind. A light tin can easily become a tight lin, for example.

The team also found that the brain seemed to split phonemes into three categories based on which part of the tongue produced them. Nature explains:

Data revealed three categories of consonant: Front-of-the-tongue sounds (such as 'sa'), back-of-the-tongue sounds ('ga'), and lip sounds ('ma'). Vowels split into two groups: Those that require rounded lips or not ('oo' versus 'aa'). [Nature]

Sounds formed in the same part of the mouth are even easier to flip-flop. This means that the neural path that leads to "Sally sells seashells" runs right alongside "Sally sells she sells." Nature:

"This implies that tongue twisters are hard because the representations in the brain greatly overlap," Chang says. 'Sss' and 'Shh' are both stored in the brain as front-of-the-tongue sounds, for example, so the brain probably confuses these more often than sounds that are made by different parts of the tongue. 'Sally sells seashells' is tricky. 'Mally sells sea-smells' is not. [Nature]

Still, it's worth a shot. Try saying, "Pad kid poured curd pulled cod" ten times fast. Go.