Why do shampoo bottles tells us to wash our hair twice? The stuff we use to clean whitewall tires (well, those of us who clean whitewalls, which definitely seems like a losing proposition) doesn’t tell us to lather, rinse and repeat. Is our hair really that dirty? Or — perish the thought — is this just a way of getting us to use up the shampoo twice as quickly?

Science? Marketing? Just good hygiene? [Tags: doep puzzle]

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