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Why is it that our hair – and for men, our beard – goes white while the other hair on our head (eyebrows and eyelashes) stays its original colour?
Guy Cox,
Sydney, Australia
JGI/Tom Grill/Tetra Images, LLC/Alamy
Why are some people very heavy sleepers, while others are woken by only a small disturbance?
Rachel Mckeown,
Cambridge, UK
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