The door opens suddenly, with Rita stepping inside unannounced. She gives a brief start when she sees Lambert and Celandine, then lets out a short breath. "So this is where you were," she says, her tone mildly accusative despite her being the one walking in on them.

Which means that was Celandine's voice just a moment ago... Rita hadn't recognized it when she heard it from outside, but now it makes sense.

"...What are you doing?" she goes on to ask, eyes narrowed at the beaker and its strange-looking contents.