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The biggest kidney stone on record weighed more than a kilogram and was 17 centimeters in diameter. The patient didn’t actually swallow a stone the size of a coconut; kidney stones form inside the body. So how do they grow in the first place? And why are they so painful to get out? Arash Shadman shares the science behind kidney stones.

Lesson by Arash Shadman, directed by TED-Ed.