Just as Pavlov's dog learned to associate the sound of a bell ringing with dinnertime, rats can learn to associate flashes of light with how long they must wait to receive a sip of water.

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Unless you've changed the default settings on your email, you are treated to a pop-up message, the sound of a bell, or a counter that signals your growing number of unread messages.

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Pavlov's early experiments on reflexes trained dogs to salivate at the sound of a bell, by ringing one every time they were fed with meat.

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But when he rigged the truck's bell to sound more like a jazz cymbal, he wound up making more money that summer than he'd made teaching for nine months.

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