What do you see in this picture?
Some people immediately see a vase or trophy (in white). Others see two faces in profile (in orange). Generally, we can switch back and forth between perceiving one and the other.
This illusion is interesting because it shows that perception is not solely determined by an image. It’s also crucial that the brain be able to separate objects from background—which, as in the picture above, can be tricky. Which is the object here, the vase or the faces? Which is the background? The spontaneous reversal between object and background illustrates the dynamism of perception.