Analysis of the linear normal modes of a finite-thickness slab shows that bending is indeed stabilized when the ratio of vertical to horizontal velocity dispersions exceeds about 0.3. Since the elongation of a stellar system with this anisotropy is approximately 15:1 — much more extreme than observed in real galaxies — bending instabilities were believed for many years to be of little importance. However, Fridman & Polyachenko showed that the critical axis ratio for stability of homogeneous (constant-density) oblate and prolate spheroids was roughly 3:1, not 15:1 as implied by the infinite slab, and Merritt & Hernquist found a similar result in an N-body study of inhomogeneous prolate spheroids (Fig. 1).