I learned that tongue twiste are execises that to can improve our pronunciation to delevop skills for a fluent pronunciation 

what are tongue twister

They serve a practical purpose in practising pronunciation. English tongue twisters may be used by foreign students of English to improve their accent, actors who need to develop a certain accent, and by speech therapists to help those with speech difficulties.

 http://www.fun-with-words.com/tong_explain.html

 Peter Piper picked a peck of pickled peppers.
A peck of pickled peppers Peter Piper picked.
If Peter Piper picked a peck of pickled peppers,
Where's the peck of pickled peppers Peter Piper picked?

Something in a thirty-acre thermal thicket of thorns and thistles thumped and thundered threatening the three-D thoughts of Matthew the thug - although, theatrically, it was only the thirteen-thousand thistles and thorns through the underneath of his thigh that the thirty year old thug thought of that morning.

In this web page there are more tongue twisters
http://www.uebersetzung.at/twister/en.htm