We show that not every Salem number appears as the growth rate of a cocompact
hyperbolic Coxeter group. We also give a new proof of the fact that the growth
rates of planar hyperbolic Coxeter groups are spectral radii of Coxeter
transformations, and show that this need not be the case for growth rates of
hyperbolic tetrahedral Coxeter groups.Comment: 23 pages, 3 figure