In medias res. Isn't it amazing?
From the seemingly random blobs a dog props out. Is it our expectation? Is it really there. I wonder how old kids can see the dog. Is it something taht is really there for every one of us?
Let me show You an advanced Kanizsa Triangle type illusion. This is most probably a low level illusion. My student research conference paper in 1998 was exactly about trying to model this kind of illusion.