The inelasticity of the critical neutron scattering in Tb was measured at and above the Neel temperature. In the hydrodynamic region the line width Gamma (q=0, kappa 1)=C kappa z1, with z=1.4+or-0.1 and c=4.3+or-0.3 meVAAz. This result deviates from the conventional theory, which predicts that Gamma (q=0, kappa 1) is inversely proportional to the static susceptibility, that is z=2. In the critical region it was found that Gamma (q, kappa 1=0)= Lambda qdelta , with delta =2.0+or-0.1 and Lambda =7.5+or-0.7 meVAAdelta . The prediction of the dynamical scaling laws that delta =z is thus not fulfilled.