A human egg cell DENNIS KUNKEL MICROSCOPY/SCIENCE PHOTO LIBRARY

We have been able to watch death travelling for the first time – and it moves in a wave at a pace of 30 micrometres per minute. At least, that is how fast death spreads across an egg cell.

In multicellular animals, cells often sacrifice themselves for the greater good. First, much of the machinery inside the cell self-destructs, and then the whole cell disintegrates. Some cells undergo this programmed cell death during development – it’s how our fingers separate in the womb, for instance – while other cells trigger it to prevent …