The discussion centers on the visual effects of two non-rotating black holes colliding, particularly under the framework of General Relativity (GR). Observers would see the event horizons of the black holes merge, but they would not directly witness the collision due to light being unable to escape from within the horizons. Instead, as the black holes approach, light from surrounding matter would become increasingly redshifted and eventually fade from view as the event horizon expands. The conversation also touches on the misconception that an observer would see objects freeze at the horizon; rather, they would appear to slow down and dim as they approach. Ultimately, the merging of the black holes results in a larger event horizon, obscuring previously visible matter.