Using a small one inch cutter (I used a bottle top), cut the central hole out of the circle, to make a ring. (betterbatter.org)
They found that the star was circled by a ring of gas with a central hole that was probably created by an unseen planet or companion star. (sciencedaily.com)
As a fish swims through the central hole, it disappears while the pondweed behind the cloak remains perfectly visible. (scientificamerican.com)