Well, some of the stretches Dira and the other dancer do are collaborative, but that can't be the whole answer because the majority aren't. They also perform some trust falls and do a bit of throwing each other around in the air before getting started.
Folder Lady counts them in and the accompanist starts a frantic introduction. Several snippets are already familiar from the warmups and from Colley's whistling yesterday, but the stylisms are very different; the player largely lets the strings ring out and the reverberation is left to overlap itself into disharmony except for key moments of staccato.
The dancers are equally wild, but clearly working around some structure not present in the rehearsal space that they're meant to be climbing up and jumping off from time to time. There are a fair number of acrobatic feats, but the impression is definitely of a dance that happens to include them when they serve what it's going for, and not of a gymnastic showcase. Folder Lady - the director, presumably - cuts them off at moderately frequent intervals to reposition an arm or nitpick a timing.
It's subtle enough that several tries go by with it being noticeable, but when she resets between takes it's a little more obvious - the other dancer is copying from the knitter and the reader as she performs. Her hair grows less lustrous and her face gains a pallor that doesn't look unhealthy on its own, but is sickly paired with her acting; when the director lets the scene run long enough she trips and falls in a way that looks legitimately accidental (and quite painful) except for the fact that everyone keeps going afterward.
Dira's character mimes offering her various invisible objects plucked from the nonexistent scenery, which resaturate and revitalize her to various degrees, all temporarily - startlingly, they begin to sing several minutes into the number. It's probably less jarring in the context of the full show; it manages to sound like a reprise even though Kyeo hasn't heard an earlier song it could be referencing. Ultimately Dira pulls something from his chest, extending the hand holding it to her, eyes on the edge of watering - and the director calls a halt to switch scenes, seeming pleased.