  A review is given of the phonon anomalies, which have been termed
``waterfalls,'' that were recently discovered through a series of neutron
inelastic scattering measurements on the lead-oxide relaxor systems PZN-xPT,
PMN, and PZN. We discuss a simple coupled-mode model that has been used
successfully to describe the basic features of the waterfall, and which relates
this unusual feature to the presence of polar micro-regions.
