maybe the mother knows the fate they will face eventually and what is going to happen to its kos and itself. so though it keeps smiling to its kos but failed to keep the sorrow in.
I'm just wondering what's defective about them. They look perfectly fine. Maybe they refused to let the hellishness of The Factory get them down, like they're the Yukkuri versions The Baskervilles or Jimmy Two Shoes? If so, I pity that poor, poor Flan. She has no idea what she's getting into.
They can just be "failures" that never learned the basics of being a pet. In a way this is more natural than pet yukkuris, who have become urbanized; domesticated if you will.