On the Russian-language Internet, I did not find almost any information about this phenomenon. There are several English-language studies of this phenomenon, but its nature has not yet been fully understood.
This is what it looks like.
When two objects come close, the shadow of the one that is farther from the light source will be attracted to the shadow of the object that is closer to the light source. In other words, a darker shadow with less partial shade is attracted to a less dark shadow with more partial shade.
When two objects come close at the same distance from the light source, the effect of attraction of shadows is almost invisible.
My explanation is this. The illusion of attraction of shadows arises as a result of a very unusual arc curvature of light, which is due only to geometry, that is, the position of objects creating shadows relative to each other and relative to the light source. But why the light is bent in this way, and under such conditions, I cannot explain.
Visually, this phenomenon is somewhat reminiscent of magnetization, gravity, or surface tension of water when it touches an object, because it occurs with noticeable acceleration. Perhaps even along with the curvature, some acceleration of light occurs.
Another explanation is that light has no speed. Light is a standing wave distributed in the ether, and the phenomenon of attraction of shadows is a kind of disturbance of the induction of light in the ether. As I could, I translated the meaning of the explanation in the next video in English.
Promotional video:
In English, this phenomenon is called the shadow blister effect.