A tongue twister is a series of words or a longer piece, like a poem, constructed to be very difficult to pronounce properly. Tongue twisters are used to create humor by challenging someone to repeat them very fast and listening to the funny results, as well as by public speakers and speech language students to increase verbal agility. Tongue twisters are also useful in understanding how we process language: they have been used in scientific research to substantiate the claim that silent reading involves articulation. It turns out that there are certain sound sequences that are difficult to alternate because of the changing positions in the mouth and/or the aural feedback of the sound similarities, and tongue twisters focus on these. Sometimes the visual appearance of the words is an added factor.
Shifting from a single sound to a blend or digraph. Shifting between /s/ and /sh/ is quite tricky, so you will find many tongue twisters that play on this sound combination: She sells seashells by the seashore. and The sixth sheik's sixth sheep's sick. In the following tongue twister, we see a shift between /k/ and two blends: /kr/ and /kl/: How can a clam cram in a clean cream can?
Changed order. Another difficult shift occurs when two words present the same sounds in the opposite order. Juxtaposing these words in a tongue twister means that we're still hearing the aural feedback and experiencing the muscle memory of saying the first sound when reading the second, and this causes confusion. Here is an example: A quick-witted cricket critic. Both words have the blend /kr/ and the single consonant sounds /k/ and /t/, but in cricket they appear /kr/, /k/, then /t/; whereas in critic, they appear /kr/, /t/, then /k/.
Similar but different. Another tricky pronunciation situation is alternating between words that are perfect rhymes -- that is, only the initial sound is different -- or words in which only the final sound is different. Perhaps it is distinguishing the differences in spite of the similarities that causes the complications in these tongue twisters. This tongue twister demonstrates both situations:
Denise sees the fleece,
Denise sees the fleas.
At least Denise could sneeze
and feed and freeze the fleas.
Homophones. Homophones are words that sound the same but are spelled differently, and the recognition of a word that looks different but sounds the same as a word we've already said seems to increase the complexity of pronunciation. The following tongue twister is attributed to Bill Waterson in an "Calvin and Hobbes" cartoon and demonstrates both homophones and perfect rhymes:
How many boards
Could the Mongols hoard
If the Mongol hoards got bored?
Various combinations. The following tongue twister employs words that are homophones; shifting initial blends /st/, /sh/, and /ch/; and perfect rhymes all in eleven words: If Stu chews shoes, should Stu choose the shoes he chews?