Koishi is referring to a 4koma that doesn't seem to be here, by the same artist, where she rips Reisen's ears off, throws them into a hot spring, ladles them into a bowl and forcefully stuffs them into Reisen's mouth. Video here for as long as the account isn't deleted.
Your little sister? You must be joking...I'm d-o-n-e!Good girl,
good girlEnjoy your meal!What the....?The moment you see Koishi's food, you'll be lost for words.I've come here before to make food for Miss Rabbit, you know!It's true that I can't give out any words...I understand your distrust... However!