Either with lightly oiled hands, latex gloves, or between wax paper, shape the popcorn into eight equal sized balls. Place on sheet of wax or parchment, then press down slightly to achieve more of a brain shape. Squeeze another drop or two of red food coloring on the top of each popcorn ball, then use a paintbrush to paint a solid red line down the center. Paint on additional "blood" as desired. Allow to cool completely before serving.