The replayed past selves inside a dream, which the dreamer and any observers watch from outside like floating ghosts.
Inside Katia's dream the past does not merely play; it walks. A second Katia, a memory ghost from about a year earlier, rushes toward the hospital door clutching a folder of papers, while the present Katia and Carl stand and watch. Carl is shocked at the contrast: the memory ghost is visibly smaller, a woman struggling with paperwork he says he would never have given a second glance, against the blazing force of nature the real Katia has become.
The watchers cannot touch anything. Katia reaches down to stroke baby Annie's face and her hand passes right through. They follow the ghosts through the hallways floating along like ghosts themselves. Sometimes both Katias speak at once, saying "No" together at the door and shouting "He had no right!" in unison. The ghosts can be disrupted from outside: Shi Maria bursts through the memory ghost of Katia and Annie when her dream collides with theirs.
Solid-looking replicas of the dreamer's past self and everyone present in the memory, intangible to observers and unaware of them.
The mechanism by which a dreamer relives and narrates a memory to a companion.