Blurry lights

When the background appears out of focus on a picture because the camera is focused on something closer, then any lights in the background appear as little glowing blobs. I saw a picture on Pinterest when somebody had covered the front of their camera lens with cardboard with a hole cut out. Whatever's shape the hole is that let's light into the camera's sensor is the shape that the blurry blobs in the background will appear. As I happen to have a heart shaped cutter, that is the shape I went for. The first picture shows the cardboard piece I put on the front of the camera, and below that you can see pictures with it taking effect! It is a bizarre but clever effect!