To Suggest Depth
This trick is as old as the hills, maybe even older. Everybody knows that things far a way look smaller. Therefore something smaller must be farther away.
And it works. It's hard to see the bird on the right as being right next to the one on the left only half the size. But if it's an actual quilt then that's what is happening.
The bird is from my 23 June 2010 post.