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Breathe deeply - what can you smell? We live in a landscape of scents - but unlike sniffer dogs, we don't have the ability to identify and read them. Until now. Scientists are training not just dogs, but bees, mice and electronic noses to sniff out security threats by odour alone. Amber Marks explores the growth of olfactory surveillance, finding out about the challenges of harnessing and mimicking nature, and asking about the implications of harnessing this world of scents.