  It is shown that during the motion of two initially gravitationally bound
spherical shells, consisting of point particles moving along ballistic
trajectories, one of the shell may be expelled to infinity at subrelativistic
speed $v_{exp}\leq 0.25 c$. The problem is solved in Newtonian gravity. Motion
of two intersecting shells in the case when they do not runaway shows a chaotic
behaviour. We hope that this toy and oversimplyfied model can give nevertheless
a qualitative idea on the nature of the mechanism of matter outbursts from the
dense stellar clusters.
