  A double-scattering reaction $\pi^+ + d\to p + p + \eta$, where an $\eta$
meson is rescattered, may provide new information on the $\eta N\to \eta N$
scattering. An idea to measure this reaction is proposed. Moreover,
experimental search for $\eta$-mesic nuclei by the same $(\pi, N)$ reaction is
discussed.
