Tongue twisters in Finnish. Couple of times I have been asked if Finnish has tongue twisters, and I have failed to remember any.

• Mun mummoni muni mun mammani, mun mammani muni mun = My grandma hatched my mom, my mom hatched me (song)
• Appilan pappilan apupapin papupata pankolla porisee ja kuohuu = Appila vicarage’s assistant pastor’s beanpot is steaming and boiling on the stove

I find the kind with lots of declinations (declensions) particularly interesting (I found the translations on the page rather poor):

• syyttämättäjättämispäätöksestään = of his/her decision to refrain from accusing (this is real Finnish, probably used in official documents and news with bureaucratic language)
• epäjärjestelmällistyttämättömyydellänsäkään ~  even with his quality of having a lack of having been made disorganized OR even with his state of having a lack of having disorganized* (something, object not mentioned; no Finn understands this intuitively and most even not after trying)

* According to Yahoo! Answers, alternative translations include “even with its quality of not being possible to be made irrational.” and “not even when taking into account his/her/its way/ability/tendency of not disorganizing” but I think they are wrong.

(Stopped using Flock after realizing YouTube does not work in it, although other Flash videos do.)