i just did a rerun of the game, my suspicion is that the scene you are thinking of doesn't have any choice, which in this case makes it awfully hard to find since you'd have to reread a lot of dialogue, or it's something else entirely and not a moo. the closest i've found was the hum or encourage option by chapter 14.
Thanks, Maybe that's the reason, I wanted to see it because I decided to play again after a long time and I remember a specific scene that happened between Asterion and the MC, where the MC said that he finds Asterion's moo relaxing and the Asterion mooed right in his ear, but now, I don't know if this scene really exists or I'm going crazy, I'll try to read the beginning again to see if I can find it, thanks for the help.