  We prove that, for a hyperbolic two bridge knot, infinitely many Dehn
fillings are rigid in $SO_0(4,1)$. Here rigidity means that any discrete and
faithful representation in $SO_0(4,1)$ is conjugate to the holonomy
representation in $SO_0(3,1)$. We also show local rigidity for almost all Dehn
fillings.
