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Last Word is Â鶹´«Ã½â€™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

Binocular vision gives us a 3D perspective, and two ears let us locate the direction of a sound. But why two nostrils?

David Muir
Edinburgh, UK

First, press your finger against the left side of your nose to close the left nostril. Breathe deeply through your right nostril. Now, close your right nostril and breathe through your left…