Q. We see an object when light from that object falls on our eyes. But many-a-times , if we think about something, we are able to see its image(though a bit hazy). We may have never seen that thing before, but still we can see it happening. Suppose, if someone tells about a bird with blue feathers,a red beak and a yellow crown, I am still able to make an image of the bird, though I have never seen it before; I can even imagine it flying or sitting on my hand or on a tree. Why does it happen?