A really weird carnival

Today is Carnival and the pupils are wearing disguises. So are all the teachers. Mr. Lombier is dressed like Charlie Chaplin. Lea's teacher is a Gypsy with flounces on her dress and castanets. But what's happened to Désiré? He's clowning around to make his friends laugh when normally he's so well-behaved and sensible. When the teacher calls him up to the front of the class, he gets sent back to his seat with a zero because he hasn't learned his text by heart. But he doesn't care! He even sticks his tongue out behind the teacher's back, as if he was making fun of her. Then he mumbles "I don't care!" Lea is worried about her pal. She wants to know what's wrong with him...