Many cellular activities are driven by complex protein machines. By measuring the behaviour of fluorescent protein fusions in real time in living cells it has become apparent that many of these complexes are not fixed, but are dynamic. To some extent this might be expected, for example, for cell division complexes, as defining mid-cell is linked to growth and cell cycle, but perhaps comes as more of a surprise with a complex anchored machine like the bacterial flagellar motor. The assumption ...