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If you wrote a word on a ball of string, then unravelled it, how challenging would it be to decipher the word?

Howard Owens, Exeter, Devon, UK

We hear about the overload of carbon dioxide in the atmosphere, but what percentage of this comes from human exhalation?

Paul Gallagher, Devizes, Wiltshire, UK

To answer this question – or ask a new one – email lastword@newscientist.com.

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