Positive use of negative space

When I was writing Who Needs Words, there came a point where I had to write about silence. After all, silence in speech, rather like white space amongst print – allows us to discern what is really there. At the time I used the illustration below, and asked whether it showed four black rectangles or one white cross.

Just today, however, someone sent me the wonderful picture below. Can you see the two faces on this handsome cow’s face?  A bit like the silence between words – the secret’s in the spaces!