EXPLANATION: You see this scene if you accept Milfeuille’s tour of the Elle Ciel and then visit the lounge where Mint is inside. Mint drinks tea, and then eats a cherry. The cherry is extremely delicious; Mint’s extra ears (that come from her heritage as a Blancmanche family member) twitch in excitement and Mint says “Oishii!” This means something along the lines of “Sweet!” It will make more sense if you realize that Mint Blancmanche LOVES sweet foods to the point of rapture.
