  Both the Szilard engine and Landauer's principle seem to raise a similar problem about the relationship between knowledge and thermodynamic entropy: if one could know which side of the engine the molecule was located, one could extract work; if one could know which logical state the device was in, one could set it to zero without work. Without this knowledge, it is necessary to design a process that acts independently of the specific state the system is in. But it is plain that this does not tell us that, even without the knowledge, it is impossible to design a clever process that can still extract the work from engine without compensation, or a clever process that can still reset the bit without work. Hamiltonian mechanics and Liouville's Theorem seems to play a vital, if largely unnoticed, role. As Zhang and Zhang's demon demonstrates, unconstrained violations of the second law are clearly possible given non-Hamiltonian flows and no appeal to information theory or computation would seem able to avoid this.