Why two shadows bend when close together

视频原地址：https://www.youtube.com/watch?v=dXNyF7lv_Wc

This is called the Shadow Blister Effect. Essentially it’s a bit of an illusion caused by two penumbras, or fuzzy regions at the edge of an objects shadow. As they overlap, they seem to bridge because the prenumbras start to mix and create a darker shaded area. The eye doesn’t consider the penumbra to be part of the shadow since its brighter than the shadow, but when they merge they are dark enough to be considered by the eye to be part of the shadow.

这叫做“”。它其实有点像幻象，因为两个黑黑的影子周围其实存在着不太明显的半影，当两个物体靠近时，其半影将融合，加深其颜色，人们看起来就像是原来的影子在互相吸引并融合在一起一样。