>>42275359Because after you get turned into a filly if you let him keep singing you won't notice your mind slowly going hazy, you won't notice when you lose critical thinking skills, and you won't notice that he's getting pretty handsy with you, but you will notice when you wake up groggily in some Ponyville back alley after an indeterminate amount of time with no recollection of what happened and cum pouring out from between your legs.