  Mutual interaction of localized nonlinear waves, e.g. solitons and modulation
instability patterns, is a fascinating and intensively-studied topic of
nonlinear science. In this research report, we report on the observation of a
novel type of breather interaction in telecommunication optical fibers, in
which two identical breathers propagate with opposite group velocities. Under
certain conditions, neither amplification nor annihilation occur at the
collision point and most interestingly, its amplitude is almost equal to
another maximum of either oscillating breather. This ghost-like breather
interaction dynamics can be fully described by the N-breather solution of the
nonlinear Schr\"odinger equation.
