Yelena knows none of this has been easy, and that Cassandra has as many issues with trust as anyone else, but there's a sort of warmth that spreads inside her chest when she accepts that simple gesture. She's someone Yelena has been looking out for since she got here, and it's nice to know, in any minor way it can be shown, that it's appreciated. That the trust is being built here between them.

She will continue their walkthrough of the house as they talk, taking a moment to pause and check out each room as they go, "So then... we could only know if we saw them cast the spell?" she's just trying to follow, and this is pretty well outside of her general realm of understanding. Magic might, to some extent, exist in her world– the Asgardians and Scarlet Witch do come to mind– but it's never been part of Yelena's life at all. No need to study up on that when she was doing the dirty work behind the scenes, usually involved with more politically or similarly minded types. Assassins and magic? Not so common a cross-over, actually.

She peeks into bedrooms as they walk through halls, "So, if there are magical recording devices, that detection spell could possibly pick up on it, yes? Would you be able to do it?" Or is her knowledge more strictly of the academic sort? These would be good things to know.