@Yaoifan Pheromones, I guess from both parents. Cheong-ho's anxiousness gives off a strange pheromone. I guess because yirim is sick and he's pheromone has also problems. Or maybe it's all on Cheong-ho. As he said, it's his fault that yi-ho is rejecting his mom. Do you notice when Cheong-ho hugs yirim and his anxiousness went down, yi-ho was staring at him with a light background and also small white dots, I guess that's because he can feel it on his pheromones. Next is when Cheong-ho leaned his head onto yirim's shoulder and realizing that yirim would never run away again, thus vanishing his anxiousness, also light background and light effect, and yi-ho was staring and feeling. Then he called yirim mama after that.