Both "buffalo" and "police" serve as enough different parts of speech to enable us to form entire sentences by simply repeating the word.
Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo.
Police police police police police police police police.
although these are basically just adjectives, verbs, and nouns.
These two sentences have identical structure (with some Buffalo capitalized because they refer to the city of Buffalo, NY). Below, the bold words are the subject and their action (buffalo from Buffalo, or "Buffalo buffalo"), the italics are another set of buffalo from Buffalo acting on those buffalo, and the plaintext is the buffalo being buffaloed (intimidated) by the original subject.
Buffalo buffalo Buffalo buffalo bufallo buffalo Buffalo buffalo.
Or, more clearly,
Bison from New York, who are intimidated by bison from New York, intimidate bison from New York.
I hope I've made it clear.
Note: In the "police" version, the structure is identical, but we are discussing "police police", or police that police other police, policing other police police while being policed by police police.