I have come across this expression before in a psychology text where it was used to draw the connection between dreams of sharks and castration anxiety.

"Symbols of oral aggression may be placed along a continuum of distance from the quality of humanness. In a dream, sharks represent the vagina dentate, or even a dentate phallus: fear of being engulfed by the preoedipal parent."

—Lane, Robert, and Saralea E. Chazan, Psychoanalytic Psychology.

You can't help but wonder at its origins. Freud? Bosch? Rabelais? Medieval bestiaries? Because God forbid it comes from an actual teratological case.