For a while, they mimic the picture perfectly, Sans-Serif curled up against his brother, who has wrapped an arm protectively around his ribcage, both of them smiling at the book, and more than that, at each other, for feeling so happy. S-4 nudges his skull against Sans-Serif's, laughing softly.

"That's all that matters, right? As long as you love someone, and you're really, really happy with them. Then it doesn't matter who we have. A mother, or a brother, or friends, or anything else."

S-4 nods to himself, like this makes perfect sense, though he hesitates a moment after. Is that really all there is to it? Or... do they need someone else to love them both? They had Sans, but Sans has been so busy lately. Gaster has disappeared. And no one else here could be like that... could they?

S-4 frowns a bit when his brother goes back to puzzling over their original question, but eventually sighs. He should have expected that his brother wouldn't be satisfied without a proper answer.

"I don't think he would have said that, no. So some birds are mothers, but, but not all mothers are birds. I guess that's probably why he asked all those other animals. Maybe they can be mothers too."