  Spatially localized exact solutions of plane Couette flow are organized in a
snakes-and-ladders structure strikingly similar to that observed for simpler
pattern-forming partial differential equations. [PRL 104,104501 (2010)]. We
demonstrate the mechanism by which these snaking solutions originate from
well-known periodic states of the Taylor-Couette system. They are formed by a
localized slug of Wavy-Vortex flow that emerges from a background of Taylor
vortices via a modulational sideband instability. This mechanism suggests a
deep connection between pattern-formation theory and Navier-Stokes flow.
