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Last Word is New Scientist’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

Why do we itch in random places? What makes this impulse manifest on, say, an elbow at one moment, but the back of a knee at another?

Rachel Loden,
California, US

Why do rainbows refract light into several different colours, but we don’t see the same effect with cloud inversions?

Tony Sandy,
Alness, the Highlands, UK

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

Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.

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