There are optical illusions and audio illusions. Is there such a thing as an olfactory illusion?
Justin Baker
Melbourne, Australia
What forces are acting on a particle of fluid that makes it start spiralling or moving helically down a pipe instead of flowing smoothly?
Phil Morey
via email
Last Word is 91av’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.comTo answer this question – or ask a new one – email lastword@newscientist.com.
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