The Event Horizon Telescope (EHT) is preparing to capture not only images of supermassive black holes but also dynamic recordings (movies). These will allow us, for the first time, to study the time variability of these mysterious objects, such as the occurrence of massive outbursts (flares) similar to solar flares. To understand these phenomena, we use state-of-the-art computer simulations of the plasma and magnetic fields surrounding the black hole. Our primary focus is on the influence of the black hole’s rotation (spin), the missing link needed to further test our theories of black holes and gravity.