gpt
Subaru:  A little after that, Subaru raised his eyebrows, remembering something. “Oh, right. Ros, there’s something I wanted to ask you. Is that all right?”
human
Roswaal:  “Weeell, if it is within my vast personal knowledge, I wooould not mind.”
gpt
Subaru:  “That’s the most roundabout way of saying ‘I’m really smart’ that I’ve ever heard. But ah, anyway, how is this bath heated?” Subaru knocked a couple of times on the bottom of the tub as he addressed what had been nagging him the whole time. The bathtub Subaru and Roswaal were soaking in was made of stone; its pleasant smoothness made him think of marble. The bath was in a corner under the mansion, and of course it was for both genders. To begin with, everything in the bath was swapped after each time, so he had no special sense of fulfillment from getting in after Emilia. Subaru added a thought. “Not that I’m boiling in here. I just noticed before I got in.”
human
Roswaal:  “From time to time, your inquisitive spirit truuuly astounds me. I wonder if it is youth…although I wonder if I would have had that thought when I was your age?” Roswaal seemed to see a rare dazzle in Subaru’s youth as he nodded. “Regardless, the answer iiis quite simple. You seeee, there is a fire-attuned magic crystal under the bathtub that heats it. When triggered by the mana of someone entering the bath, it activates and brings the water to a boil. Surely you used such a thing in the kitchen?”
gpt
Subaru:  “So that’s how that pot worked. I was wondering how you cooked here without gas.” After Rem had made brief use of it, it’d been Subaru’s turn to peel vegetables.