  An analytic method is given for deriving the part of the retarded Green's
function v(x,x') that contributes to the tail term in the radiation reaction
force felt by a particle coupled to a massless minimally coupled scalar field.
The method gives an expansion of v(x,x') for small separations of the points x,
x' valid for an arbitrary static spherically symmetric spacetime. It is
obtained by using a WKB approximation for the Euclidean Green's function for
the massless minimally coupled scalar field and is equivalent to the
DeWitt-Schwinger expansion for v(x,x'). The first few terms in this expansion
are displayed here for the case of Schwarzschild spacetime.
