What does stuffing one's own vagina with a potato indicate about the stuffer? Writer/director (below) Claudia Llosa's THE MILK OF SORROW (La teta asustada) tells us some facts, in chunks of exposition, but indicates more via the alternately withdrawn /florid performance of Magaly Solier (left), whose beauty steals men's hearts (and the viewer's) even as her bizarre behavior quickly pushes most of them away.
For one thing that potato pretty well prevents coitus, which is certainly the original intent -- which the character, Fausta, has learned from her mother (the two are shown below) who was raped repeatedly back in the bad old days of Peru. We north-westerners know a bit about Chile under Pinochet and Argentina's "disappeared," but of Peru's dictatorial history, not so much. We won't learn a lot here, either, but the bits and pieces we pick up from the film will give us, at least, an idea.
The potato also represents a symbolic barrier -- to intimacy, friendship, feelings and more. As it grows its finger-like, projectile eyes, as a doctor in the film so ingratiatingly explains, it infects its host, sickening and weakening her. Holding on to the past, as we are later told, is not healthy. But after growing up with a mom like Fausta's, it's a little difficult to let go.