Weiss and, independently, Mazzeo and Montcouquiol recently proved that a 3-dimensional hyperbolic cone-manifold (possibly with vertices) with all cone angles less than 2π is infinitesimally rigid. On the other hand, Casson provided 1998 an example of an infinitesimally flexible cone-manifold with some of the cone angles larger than 2π. In this paper several new examples of infinitesimally flexible cone-manifolds are constructed. The basic idea is that the double of an infinitesimally flexible polyhedron is an infinitesimally flexible cone-manifold. With some additional effort, we are able to construct infinitesimally flexible cone-manifolds without vertices and with all cone angles larger than 2π.
Ivan IZMESTIEV. "Examples of infinitesimally flexible 3-dimensional hyperbolic cone-manifolds." J. Math. Soc. Japan 63 (2) 581 - 598, April, 2011. https://doi.org/10.2969/jmsj/06320581