Is He a Girl? - Louis Sachar - Bog

Marvin is yet again caught in a dilemma. He's been told that he'll turn into a girl if he kisses his elbow, and after accidentally doing just that he wonders if it is really going to happen to him. His voice starts to change, and he even dots his 'i's with a heart in class! What on earth has happened to Marvin, and will he ever be the same again?