In making-it-move news this week: weaponized spirulina platensis (make-it-move part XIX here) as reported by Li Zhang in Science Robotics (DOI) and the first microswimmer featured in this blog applied in an actual biological system! Spirulina is a microalgae with a natural helical shape and also with natural fluorescence. To prepare this swimmer for microswimming it was dip-coated with iron oxide nanoparticles and then annealed. The original swimmer has by then disintegrated (sorry!) but what is left, a solution of 100 micrometer long magnetic screws can be injected and by virtue of external magnets moved around at will. For this the helical shape is essential. Also importantly the particles are superparamagnetic, a residual magnetic strength would cause them to clutter to together with disastrous consequences. Navigation, fluorescence-based medical imaging and magnetic resonance imaging was demonstrated to track the particle swarm. As a peculiar experimental result the swarm was found to be cytotoxic towards cancer cells. But how? Iron oxide is not cytotoxic. The article concludes that residual spirulina from inside the helix is responsible.