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Have you ever been to The Mystery Spot[1]? It is a fun tourist trap with all sorts of conundrums like that.

[1]: https://www.mysteryspot.com/

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obviously a small space-time anomaly. Nothing to be alarmed about. Sapphire and Steel have been assigned.
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This is the answer we came up with. Guy in the flat downstairs must have been dicking about with supermassive dark matter.
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