His sister had placed her son Perdix under his charge to be taught the
mechanical arts. He was an apt scholar and gave striking evidence of
ingenuity. While walking on the seashore he picked up the spine of a
fish. Imitating it, he took a piece of iron and notched it on the edge, and
thus invented the saw. He put two pieces of iron together, connected
them at one end with a rivet, and sharpening the other ends, made a
pair of compasses.
Which trait from the character wheel is used in this paragraph to describe
Perdix?