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If you squint hard enough, the capital letter pi (Π) looks like half a circle.
(discuss.tchncs.de)
A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. The best ones are thoughts that many people can relate to and they find something funny or interesting in regular stuff.
https://en.m.wikipedia.org/wiki/Pi