Cubic cadmium(II) cyanide is amongst the most important isotropic negative thermal expansion (NTE) materials, with behavior more than twice as extreme as that of better known systems such as ZrW$_2$O$_8$. We investigate the relationship between the geometrically frustrated orientational order of the molecular CN$^-$ anion the system’s lattice dynamics. Inelastic neutron scattering (INS) is reported on the system approaching the cyanide order-disorder transition from above and displays non-trivial mode-softening over a wide range of temperatures associated with the correlated cyanide order. The simulation of lattice dynamics in systems with correlated disorder is involved: supercell lattice dynamics (SCLD) are used for simulations on a simple model system. Simplifying approximations are investigated towards the goal of reproducing the INS measured, and understanding the significance of correlated disorder in the NTE mechanism.