At our last Metolius Fish-in, when I ran out of cheetos and couldn't find any more salmon/stone flies to feed to the monsters at the bridge, I experimented with other odds & ends. The materials which floated ON the surface were totally ignored. The materials like twigs with legs which went through the surface film were hammered (THEN spit out). On the film isn't always best. Maybe that is why the ugly flies fish best?