"Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo." is a grammatically valid sentence in the English language, used as an example of how homonyms and homophones can be used to create complicated linguistic constructs. It has been discussed in literature since 1972 when the sentence was used by William J. Rapaport, an associate professor at the University at Buffalo. There is nothing special about eight "buffalo"s; indeed, a sentence with "buffalo" repeated any number of times is grammatically correct.
After the break is a video further explaining the grammar that constructs this sentence.