What makes an idea, a brand, or a behavior catch fire? This hour, TED speakers explore the mysteries behind the many things we spread: laughter and sadness, imagination, viruses and viral ideas.

1. Sophie Scott: Why Is Laughter Contagious?

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2. Seth Godin: What Makes An Idea Go Viral?

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3. Bill Gates: How Can We Prevent The Next Global Health Epidemic?

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4. Nicholas Christakis: How Do Our Social Networks Affect Our Health?

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5. Yuval Harari: Why Did Humans Become The Most Successful Species On Earth?

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