I can only guess it's Yuyuko complaining about Youmous babaric way of eating melon. She suggests Youmou to "use" her sword (to cut it into slices) wherein Youmou misunderstands.
Well, it is rather refreshing to see things like this instead of the really old and worn shtick of Yuyuko inhaling food.
slurpNow that you mention it, I did!crunchOh...gobbleOur knives are too short so I can't cut it properly...slobberchompWell......You used to have a long one didn't you?gulpDon't your hands get all sticky?!!!Such horrible manners...nom