Little Spirou comes out of the dentist’s with his jaw so swollen up, he can’t speak… He tries to find a way he can avoid his new look making him the laughing stock of the whole school: he'll tell people he's the guinea pig for a secret scientific experiment, or that he's wearing a mask, or even that he's been speaking very sophisticated French, which requires a lot of jaw work... Mamy's extra sticky biscuits end up providing a wonderfully timely way to cover up the truth!