Stein is not really listening to Marie as they walk to his home. He hears her chatter and dredges up the appropriate replies -- appropriate for him, anyway. Spirit would never warn a woman she might get chopped into bits if she stayed as his home. But it's an honest warning. Marie has such lovely skin and an interesting soul. Dissecting her is tempting.
But the children -- Maka and Soul -- are more tempting. He has his suspicions about Maka's ability to purify black blood, has enough evidence that he should go to the Reaper with them, but he's selfish. He wants to test his theories, and now that Spirit is no longer his weapon?
Well, now that Spirit is no longer his weapon, he doesn't have to worry about their resonance giving Spirt an inkling of the experiments he wants to perform on Maka and Soul. They're not as damaging as what Medusa subjected Crona to -- and Maka and Soul are resilient children -- but still, Spirit would not approve. At least now Stein doesn't have to worry about keeping his desires out of the range of their resonance. He just has to worry about Spirit's surveillance.
And Marie's presence. He knows what the Reaper is trying to do. Marie wants a husband, a family, a normal human life. He can feel it, and he hasn't even used her since the Reaper assigned her as his temporary weapon. It's insulting that the Reaper thinks she will tame him.
But she will distract him, and maybe that's the Reaper's true purpose. She's here, directly in front of him, and she's something he doesn't fully understand. He can't resist a puzzle. Especially in this state, balanced so precariously. Scientific inquiry both separates and connects him to people, and right now, it's his strongest connection, even stronger than his fear.
"Ah, of course." Marie takes in his lab, the specimen jars, the workbench. "I'll have to find my own apartment soon, huh? This isn't very homey."
Yes, she will have to find her own place soon. She won't be the thing absorbing all of his focus then. Just what is it about a husband and family that makes it her greatest need? What is it in her soul that gives her that desire? He's itching for his scalpels and instruments. He's itching for her to sleep so he can experiment.
She'd look so lovely on his examination table. Medusa -- her serpent arrow at his throat, immobilized by his soul threads, the stitches even and precise and perfect -- hovers before him, her manic grin slicing across her face.
Ah, Marie isn't quite as lovely as that. As horrible as her methods, as unacceptable as her ambitions were, Medusa had been a scientist. She had almost understood.
Stein's still human enough to wonder what he would have done if she had understood. Joined her? No, it wouldn't have lasted. He'd try to dissect her, she'd try to torture him, and as glorious as it would be, it would end. Once a scientist solves a puzzle, it loses all fascination.