Sandre is also keeping half a metaphorical eye on Corona's room through the wall that separates them. But it looks like Corona and Harley are just cuddling, so after a while, he stops checking on them so frequently.
This is a mistake.
Aelise wears shoes that make a very distinctive, echoing sound on the tiled stone floors, and she doesn't visit Chelsa's friends very often. The sound of her walking down the hall in a hurry is both unmistakable and unexpected.
Chelsa obligingly cuddles Sandre until she hears Aelise's footsteps, and then she gets up and peers out into the hall. "Aelise?" she asks, puzzled.
"Our new guest has an interesting talent," she says. "I'd like to ask him about it."
"All things considered," says Aelise, "I think you'll be happier if you leave them to me for now."
"...All right," shrugs Chelsa, and she goes back to her Sandre-cuddles. He's so cuddleable.
...And is confused.
There's Aelise and Corona and Harley; Harley is the one who's screaming. Aelise is using her Gift on him. Sandre can't see her Gift, not properly, but he can see its effects - the way people wither or bloom from the cellular level on up. Harley is withering.
Then he stops withering. Stops living.
Something unfamiliar happens - like fire without the heat, except not really like fire at all - and Harley's back, unwithered, good as new.
Sandre is even more confused.
Chelsa decides to let whatever just happened filter to her at some more convenient time. Aelise has good judgment about these things.