At the bottom left: The mystery of why, when I know I needed to be asleep an hour ago, I decide it's a good time to read through every Wikipedia article in the categories 'Out-of-place artifacts', 'Earth mysteries', 'Anomalous weather', and 'List of people who disappeared mysteriously'.

"Mysteries", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License

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At the bottom left: The mystery of why, when I know I needed to be asleep an hour ago, I decide it's a good time to read through every Wikipedia article in the categories 'Out-of-place artifacts', 'Earth mysteries', 'Anomalous weather', and 'List of people who disappeared mysteriously'.