Every year, tens of thousands of people have brain surgery without a single incision: there's no scalpel, no operating table, and the patient loses no blood. Instead, this procedure uses a machine that emits invisible beams of light at a precise target inside the brain. So how exactly does this treatment work? And what does it do to the tumors it targets? Hyunsoo Joshua No explains radiosurgery. [Directed by Hype CG, narrated by Addison Anderson, music by Gabriel Maia].