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Authenticity was the watchword at Behaviour, the ongoing Arches festival of live performance, when arts collective Gob Squad led the audience on a shared pursuit of fact, fiction and the nature of identity that finished just in time for New York's Ann Liv Young to put herself – and the performer/audience relationship – on the line as she ripped the guts out of myths about mermaids.

Gob Squad are the less obviously unnerving. They know we hate audience participation yet onlookers somehow find themselves wearing headphones and following instructions, speaking text, engaging with strangers. As they 'become Gob Squad' intriguing truths about our everyday performances and role-playing emerge, albeit with humour. It's a superbly crafted, complex piece of provocative strategy that sticks in the mind.

Cue Young: lolling in a paddling pool, bare-breasted, with a silvery mermaid's tail and three sailor-suited assistants at her beck and call. Just about everyone, front rows especially, will get drenched. There will be strops – rehearsed? Real? – as Young demands technicians fulfil her exact demands. Finally the show will stop mid-action, rather than end. But, and this is what makes her both icon and iconoclast, Young nails the mythic allure of the mermaid/siren sex object: spitting stinking fish at it and us inbetween pop songs that ramp up the raunch factor Young astutely links to the sexualising of unavailable females, be they Disney cartoons, under-age starlets or mermaids. Fearsome stuff.