Lyndon Johnson's 'Daisy' ad, which changed the world of politics, turns 50

Washington (CNN) - The screen is black and white.

A little girl, no taller than the weeds that surround her, stands in a field and picks petals from a delicate daisy. She quietly counts each one.

Suddenly an ominous voice can be heard counting down from 10. She looks up as the camera zooms in on her face, all the way into her iris. And then the unthinkable happens: A mushroom cloud.

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