The "Open Throat"
The greatest of all tenors, Enrico Caruso, once advised a young Italian—American soprano named Rosa Ponselle (who became one of the greatest sopranos of the 20th century) to try to sing as though there were a “square” in the back of her throat. Caruso was not simply offering a metaphor or an abstract guiding principle to help her sing better: he was telling her that she must keep her throat open, physically open, when she sang.