Language geeks might enjoy this.

There are real, grammatically correct sentences, with legitimate meanings, that consist of one repeated word or sound. Example:

"Buffalo buffalo buffalo Buffalo buffalo buffalo Buffalo buffalo."

The key in this example is to realize that Buffalo can be an animal, a city, or a verb.

Similar constructs:

"Dogs dogs dog dog dogs."

"Police police police police police."

It's not just English. Spanish:

"Como Como? Como Como Como!"

Some variants allow several words:

"Boston cats Boston-chase Boston mice Boston rats Boston-eat."

French: "Le ver vert va vers le verre vert."

Dutch: "Toen wij in Baden-Baden baadden, baadde Baden-Baden in de zon."

Mandarin Chinese: "Shī Shì shí shī shǐ" and "Shíshì shīshì Shī Shì, shì shī, shì shí shí shī. Shì shíshí shì shì shì shī. Shí shí, shì shí shī shì shì. Shì shí, shì Shī Shì shì shì. Shì shì shì shí shī, shì shǐ shì, shǐ shì shí shī shìshì. Shì shí shì shí shī shī, shì shíshì. Shíshì shī, Shì shǐ shì shì shíshì. Shíshì shì, Shì shǐ shì shí shì shí shī. Shí shí, shǐ shí shì shí shī shī, shí shí shí shī shī. Shì shì shì shì."

Explanations, and more:
The Most Confusing Sentence in the World Uses Just One Word

A History of the Sentence 'Buffalo buffalo buffalo buffalo buffalo.'