  We examine the interactions of a black hole with a massless scalar field
using a coordinate system which extends ingoing Eddington-Finkelstein
coordinates to dynamic spherically symmetric-spacetimes. We avoid problems with
the singularity by excising the region of the black hole interior to the
apparent horizon. We use a second-order finite difference scheme to solve the
equations. The resulting program is stable and convergent and will run forever
without problems. We are able to observe quasi-normal ringing and power-law
tails as well an interesting nonlinear feature.
