It’s all so sudden.

The victim is on the left side of the screen—a single-celled little pulse of life, floating about in pond water somewhere. It’s got these little hairs called cilia. You don’t see them at first. They can turn into oars. Oars for escaping.

But it doesn’t know.

The killer comes in from the right, turning lazy circles in the water, like nothing’s going on. But that’s an act. As we’ll learn later, it is getting into position, moving close, finding an angle so it can point its … its what? I see no weapon. Does it have a weapon?

“I don’t know about this exact type of ciliate,” microbiologist Patrick Keeling wrote me, “but I know about other similar predators,” and