While studying the brain's speech-planning processes, researchers found that Americans find it hard to repeat the phrase "pad kid poured curd pulled cold".
For research proposes, lead researcher Dr Stefanie Shattuck-Hufnagel, from Massachusetts Institute of Technology in Boston, asked participants to repeat the tongue twister 10 times at a fast lick, News.com.au reported.
The study found that many of the participants clammed up and stopped talking altogether.
