Matrix and Cartesian Dualism
Trust David Chalmers to come up with (tormentingly) intriguing thought-experiments!
From wikipedia entry on Dualism: "David Chalmers recently developed a thought experiment inspired by the movie The Matrix in which substance dualism could be true: Consider a computer simulation in which the bodies of the creatures are controlled by their minds and the minds remain strictly external to the simulation. The creatures can do all the science they want in the world, but they will never be able to figure out where their minds are, for they do not exist in their observable universe. This is a case of substance dualism with respect to computer simulation."
For Chalmer's original formulation of it, see Note 6 of his paper The Matrix as Metaphysics: "It is interesting to note that the Matrix Hypothesis shows a concrete way in which Cartesian substance dualism might have turned out to be true. It is sometimes held that the idea of physical processes interacting with a nonphysical mind is not just implausible but incoherent. The Matrix Hypothesis suggests fairly straightforwardly that this is wrong. Under this hypothesis, our cognitive system involves processes quite distinct from the processes in the physical world, but there is a straightforward causal story about how they interact...."