  On-shell methods have revitalized interest in scattering amplitudes which
have, in turn, shed some much needed light on the structure of quantum field
theories. These developments have been warmly embraced by the particle physics
community. Less so in the astrophyical and cosmological contexts. As part of an
effort to address this imbalance, we illustrate these methods by revisiting two
classic problems in gravity: gravitational light-bending and the vDVZ
discontinuity of massive gravity.
