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Last Word is Â鶹´«Ã½’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
In winter, birds often sit quietly on a branch for hours. Do they actually sleep more or is it just a way to conserve energy?
Caroline Deforche
Lichtervelde, Belgium
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Why do we scream in fear? It doesn’t help and it makes us more vulnerable to predators.
Chadi Ajaj
 Ottawa, Canada
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