I liked this graphical example of black hole formation posted by PAllen in another thread and I want to discuss it. It is not unusual that arguments defending existence of black hole go like that: 1. Assume that BH exists. 2. Then observer falling into BH ... I think that point 1. is begging the question fallacy. So any argument defending BH should be about formation of BH. Therefore I think that this example of PAllen is excellent basis for discussions around black holes and so it is worth a closer look. Now about example. Let's say that we are looking at star at the far edge of collapsing cluster. Let's assume further that we have idealized situation where light from that star is going exactly through the cluster's center of mass. That particular star will be gravitationally lensed (amplified) and it is a bit unclear if it will be redshifted or blushifted as it is moving toward us not away from us, right? Another point is where exactly formation of event horizon starts? It does not appear at once but is expanding from some point by engulfing mass. So we have to have some seed black hole that is produced in collision of two stars near cluster's center of mass, right?