I was sitting alone in darkness when one of them wandered in. You know the type, always popping along with another specimen. I'd seen him many times before – he'd spent the entire night with me on several occasions. He knew exactly which buttons to press.

He fired me up and mounted the specimen. I zeroed in and focussed. A collection of circles, about 10 μm across. I scanned down in 0.1 μm steps. Spherical cells, with one pole much brighter than the other. He set me to scan like that every hour and left. No problem – I'd just had a state-of-the-art ZX463 laser fitted, and it was an opportunity for me to put it through its paces.

In the middle of my 13th scan, he returned. The spheres had now elongated into capsules, with the bright signal at...

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