The classic pickled-pepper tongue twister, four lines that get harder to say the faster you go. Better as a race than a quiet read, and endlessly replayable.
From Mother Goose / Nursery Rhymes (traditional). See the whole collection.
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?
Public domain. Text from The Real Mother Goose (Blanche Fisher Wright, 1916), via Project Gutenberg. View the source edition