This is a qualitative sketch of a proposed model for SN2010mc. Panel A shows the supernova on the day it detonated. An inner shell (purple) represents the material ejected by the precursor star about one month earlier from the penultimate outburst. An outer shell (orange) is made up of material ejected by the precursor star prior to the penultimate burst. Panel B shows SN2010mc at day five. The supernova shock front (grey line) is moving at 10,000 kilometers per second, ionizing the inner and outer shells along the way, producing the broad and narrow hydrogen emission lines that astronomers on Earth detect. Panel C shows the object at day 20, when the supernova shock engulfs the inner shell. At this point, astronomers only detect a narrow hydrogen emission line.