The mouth fulfills many functions, some of which are vital to our existence, but it is also used for kissing and making love. Lili meets with doctor Tareck Ayad to understand this complex organ. She continues her quest for knowledge with French writer and essayist Alexandre Lacroix, who shares his views on kissing, and with Nicholas Charbonneaux, actor and stage director, who helps Lili as she tries to discover her sexy voice.