I think that's just the silhouette illusion[1]. In this case likely abetted by the framing elements moving near the edges. [1] - https://en.wikipedia.org/wiki/

I think that's just the silhouette illusion[1]. In this case likely abetted by the framing elements moving near the edges. [1] - https://en.wikipedia.org/wiki/Spinning_dancer https://en.wikipedia.org/wiki/Spinning_dancer