Centrosomes, the major microtubule-organizing centres in animal cells, each comprise two centrioles and a surrounding cloud of pericentriolar material(PCM). The PCM contains a filamentous `centromatrix' plus additional proteins such as centrosomin (CNN) and is often thought to be a static structure. Thomas Kaufman and co-workers show that it can in fact be highly dynamic (seep. 4707). Imaging CNN-GFP fusion proteins in live Drosophila embryos, they demonstrate that particles containing CNN and another centrosomal protein, D-TACC, oscillate radially back and forth from the centrosome. These `centrosome flares' are cell cycle regulated: flare activity decreases during metaphase, increasing again at telophase. The authors show that interfering with microtubule dynamics inhibits flaring, concluding that the process is driven by association of CNN with dynamic astral microtubules. Interestingly, during mitosis, the flares extend only as far as the actin cages surrounding the spindle; moreover, disruption of the actin cytoskeleton increases the distance flares travel, allowing them to jump to neighbouring centrosomes. The flares thus appear to be limited by the actin cage and might play a part in organizing its boundary.