Try and say “she sells sea shells by the sea shore” three times very fast. The first time might go alright, but on the second or third go-round, chances are the words start to degrade as you’re saying them, falling apart in your mouth like a crumbling Jenga tower.
Tongue twisters are nearly universal: Almost every language has its own phrases that turn people’s mouths to mush.
There’s an extra twist to tongue twisters, though. In 1982, husband-and-wife researchers Ralph and Lyn Haber ran an experiment where college students silently read sentences containing tongue twisters and similarly complex sentences without them both silently and aloud. They found that the students took longer to silently read the tongue twister sentences than the control ones. If tongue twisters slow people down and trip them up when they’re reading them silently—other research has shown that this is, again, nearly universal, even in logographic writing systems like Chinese, and when deaf people encounter tongue twisters while reading—then the problem maybe isn’t in the tongue itself, but the brain.
Another experiment by researchers at Carnegie Mellon University had people silently read tongue-twisting sentences and control sentences while inside an MRI machine. The brain scans showed that tongue twisters slowed the subjects down and affected their comprehension of the sentences—and identified the different areas of the brain activated during reading. The areas affected suggest that tongue twisters cause problems in the planning, control and/or representation of internal speech by creating a bottleneck in phonological (relating to the pattern of sounds) or articulatory processing that requires additional time and effort to parse the sounds and resolve the confusion.