Exchange information about V4641 Sgr, an extremely rare microquasar whose flickering activity can be visually observable. The object is known to harbor a black hole, and the source of the flickering visual light comes from the vicinity of the black hole. V4641 Sgr underwent a totally unexpected giant outburst reaching a binocular magnitude. cf. http://www.kusastro.kyoto-u.ac.jp/vsnet/gmsgr.html (VSNET page). Up-to-date information from VSNET will be also delivered.