So Knuckles invited Rouge the Bat to a cave near Mushroom Hill to show her the pretty glowy Mushrooms that grow there. He was going to warn her that they are not edible but then thinking in his strong mean muscle mind, he decided to tell her to go ahead, there edible, but now he remembered what they do when you eat a lot, effects the body and anything in contact with the body makes her grow, and her clothes were the closes in contact.