docs: def make_bd(self):
          "Make a set of 'shaped' random #'s for particle brightness deltas (bd)"
          self.bd = concatenate((
              # These values will dim the particles
              random.normal(
                  self.bd_mean - self.bd_mu, self.bd_sigma, 16).astype(int),
              # These values will brighten the particles
              random.normal(
                  self.bd_mean + self.bd_mu, self.bd_sigma, 16).astype(int)),
              axis=0)