A crew of four in search of an island halts in the middle of the sea to check its course. One of the two women gets off the boat for a quick swim. She spots a shark and runs for cover, only to encounter a zombie (under the sea!). She evades them both to get back on the boat and, in the process, ends up pitting the two man-eaters against each other. We have here, cinema reduced to a scientific method. We identify with the woman in the scene (not just because we empathize with her and want her saved, but also because the rewards of horror are sweetest when delayed) and are hence hostile towards both the shark and the zombie. Our emotional investment is the scene comes to an end once the woman gets out of the water and this ensuing fight becomes a pure spectacle to be relished from a safe distance, without taking sides. (This configuration is a regular in horror movies, where the threat is frequently non-thinking, neutral). The woman becomes a catalyst and makes possible reaction between elements otherwise inert and immiscible, a stimulus galvanizing a stable system into instability, a intermediary algebraic variable to be added and subtracted to an equation to make solution easier. Genre cinema at its exploitative best.