 We can see the picture as either a rabbit or a duck. It is easy to discover both readings. It is less easy to describe what happens when we switch from one interpretation to the other. Clearly we do not have the illusion that we are confronted with a “real” duck or rabbit. The shape on the paper resembles neither animal very closely. And yet there is no doubt that the shape transforms itself in some subtle way. (Gombrich 1960: 5)