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Why do people throw their heads back when experiencing ecstasy, agony, laughter, grief and surprise?

Rachel Loden,
Palo Alto, California, US

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If the world exploded, what proportion of the rocks floating in space would have evidence of life?

Tom Frost
Brisbane, Australia

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Last Word is New Å®ÉúСÊÓƵ’s long-running series in which readers give scientific answers to each other’s questions, ranging from the minutiae of everyday life to absurd astronomical hypotheticals. To answer a question or ask a new one, email lastword@newscientist.com

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