Six Slippery Snails
Notice the sounds
Move directly from /s/ into /l/ in slippery, slid and slowly, and into /n/ in snails. Avoid inserting an extra vowel into those clusters.
Words in this expression
Source
Games for All Occasions, Mary E. Blain (1909), Tongue TwistersPublic domain in the United States; the pinned source includes the Project Gutenberg license.