One of the first thing you learn in photography is that you have to focus. If you don't everything will be blurry. Thats because a camera can't capture only the light at one point. This effect is called "Depth of Field" or DOF. But this can also be used as an technique in making your photographies more interesting to the viewer.
In this exercise we had to play around with the focus. carefully putting one object in and one out of focus. In the next picture we had to take the first object and reverse the focus. We repeated this a few times. And so this came out.