To help out their tragically non-rhotic guest, my friends in San Marino made me practice this tongue twister:
Trentatre trentini entrarono trotterellando
in Trento, tutti e trentatre trotterellando.

After mastering that one, my nonna then rattled off half a dozen others that she had to learn at school, each one designed to practice a certain consonantal construction. I was very taken with the idea of using tongue twisters for a practical purpose, rather than simply for amusement. I did, however, decline to attempt any of the additional ones demonstrated for me.