© Joel Clifton

How do women make themselves heard? How do they speak on their own terms? These are the questions rattling around in Mouthpiece, a harmonic performance piece designed for two female voices. It's the best tumbleturning text since Christopher Brett Bailey's motormouth monologue This is How We Die.

Written and performed by Amy Nostbakken and Norah Sadava, Mouthpiece races through an internal monologue, the voices in one woman's head. She's sat in the bath, soaking in silence, bracing to write her late mother's eulogy – but how? What to say? It's not just that new grief pulls her thoughts in every direction at once, but that the mere idea of summing someone up in words seems impossible. A woman too. How do you eulogise your mother without reducing her to a mother? How do you convey a strong woman without letting softness slip? Language itself starts to feel like an oppressor as the piece goes on; a system that pins women in place.

The text itself is a headspin: a soundcloud of snatched conversations and radio ads, phone calls and memories. It's brilliantly written, with a slight Laurie Anderson-ish tone of voice, but it's superbly performed. Nostbakken and Sadava are the vocal equivalent of synchronised swimmers. Performing in white swimsuits – a potent act that pits their voices against their bodies, words against looks – they spring and snap into all these different voices. It's quite virtuosic.

Because Mouthpiece is as much about the female voice as it is language. One science-y speaker rattles off a reminder that voices are bodily: the sound is a symptom of one's physicality. Each voice we hear expresses character. There are mousey little squeaks, snatching sniffles between sentences; deep, definite commands pushing advice and breathy sing-song sirens like Marilyn Monroe. You hear a person's personality before you see it; how they carry themselves; how confident they are. The two are totally entwined. No wonder that getting the funeral's look right – the right eulogy dress, the right flowers, the right coffin – feels so much more pressing than writing the words.

There's a lot going on – often too much to take in. That, in itself, is mightily meaningful. It's as if Nostbakken and Sadava almost drown themselves out. The weight of anger in Mouthpiece, the frustrations beneath and the need to firefight on all fronts, is its own kind of overload. Even their speaking in sync says a lot. Their voices echo in stereo, stronger together than either would be alone. It ends with an alarming image – one of many. Two women fight over a microphone, pulling each other back in turn, so that neither speaks and silence stretches out.

Mouthpiece is an excoriating performance piece; an evisceration of the way women are gagged and voiceless. It's a gauntlet of a show: Speak Up! Listen In!

Mouthpiece runs at Canada Hub @ King's Hall, until 27 August, 3.30pm.

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