  A Galileon field is one which obeys a spacetime generalization of the
non-relativistic Galilean invariance. Such a field may possess non-canonical
kinetic terms, but ghost-free theories with a well-defined Cauchy problem
exist, constructed using a finite number of relevant operators. The
interactions of this scalar with matter are hidden by the Vainshtein effect,
causing the Galileon to become weakly coupled near heavy sources. We revisit
estimates of the fifth force mediated by a Galileon field, and show that the
parameters of the model are less constrained by experiment than previously
supposed.
