So in order to explore what this means, they become as the famously camera-shy performer, swapping roles, fitting neatly into each other's clothes—Raedie exacting a prim, yet no nonsense Lucy; Lucy slouching in typical teen stance, rolling her eyes and groaning, “Oh, goooood, I can't believe you're doing thiiiis.” Clothes are neatly folded, or flung onto the floor. They wrestle; bicker about what leeway Sia would give her kids, spin, squirm, and carry one another on their backs. They're of a similar height, and it seems, weight too. Thus, the generation gap is plugged- there is a sense that both are as stubborn and free-spirited. We are arguably most ‘ourselves’ around our families. It's not a male/female thing that the duo scrutinise, but rather a celebration of the bonding process, in all of its messy glory.

The finest moment is when they emulate the iconic scenes from Sia's controversial videos which feature teen dancer Maddie Ziegler, such as “Chandelier” and “Big Girls Cry.” This works, precisely because Ryan Heffington's choreography seems ‘genderless,’ blurring sexes as it taps into human frailty, with gestures like stomach rubbing, head shaking in circular motions, clenched fists, kicks and defensive curling up into an hedgehog-like ball, spikes out against the world. Heffington plays fast and loose with the conventions of contemporary dance, as anyone who has seen his playful short film showing how to dance to “Chandelier”will know.

There is a nod to the “Elastic Heart” video featuring Shia LaBeouf, which famously pitted the young girl against the adult Hollywood actor, roaring at each other like animals in a cage, fighting, and the discomfort at the age gap between two performers—only here, the ones taking centre stage are related by blood, with the kind of intimacy only parents and offspring can share.

They emulate Ziegler's glitchy twitchy gestures, all swept fringes and Vogue-esque ‘90s ballroom’ restless fidgety digits. They throw chairs around in a tantrum, and strut around like tyrants—little despots, both. Lucy flings her son around with wild abandon, and there's an unwieldy quality to their “Titanium” routine, the kind that you would uninhibitedly try out on a bedroom floor with your little school friends, before the awkward vagaries of puberty replaced self-confidence.

On a video screen behind them, they are lip-synching to Sia songs, stomping like the grunge militia to The White Stripes' “Seven Nation Army,” and chewing ‘gum’ which is revealed to be pieces of paper carrying slogans which allude to their individual strengths. The problem is that neither Sia's influence, nor the routines, are weighty enough. Everyone is fully aware of the attendant tensions and complexities of mother and son relationships: this “Ballad” is tuneful enough, yet it only skims the surface.

It may be somewhat slight, then, padded with repetitive moments (like the wrestling and chasing around the room) which often seem superfluous, and more than a little frustrating, but it is made with love and affection—and for many of the mothers and fathers in the audience tonight, it seems to chime with their experiences of parenthood. For its flaws, the performance is always emotionally articulate. Lucy and Raedie are calling a heartfelt truce on their respective differences, with a ‘got your back.’