It is a classical fact that the vertical component of an infinitesimal isometric deformation (IID) of a paraboloid of revolution is a harmonic function. In this talk we prove a discrete analog: the vertical component of an IID of a polyhedron inscribed in the paraboloid is a discrete harmonic function, with respect to the cotangent Laplacian. Similar, but less known is the fact that the radial component of an IID of a spherical domain is an eigenfunction of the spherical Laplacian. We establish a discrete analog: the radial component of an IID of an inscribed polyhedron is an eigenfunction of the discrete spherical Laplacian. The talk is based on a joint work with Roman Prosanov.