  We study the leading long-distance attractive force between two holes in a
plate arising from a scalar field with Dirichlet boundary conditions on the
plate. We use a formalism in which the interaction is governed by a non-local
field theory which lives on the two holes. The interaction energy is
proportional to Q_1 Q_2/r^7 at large separation r, where Q_1 and Q_2 are
certain charges associated with the holes. We compute these charges for round
and rectangular holes. We show that the 1/r^7 behavior is universal for
separations large compared to the linear dimensions of the holes, irrespective
of the spin or interactions of the bosonic field. We also study the interaction
between two long thin slits, for which the energy falls off as 1/r^6.
