Questions about example sentences with, and the definition and usage of "Serrated"

A: serrated = with uneven edges, like the edge of a car key
lucite = hard, clear plastic

She touched the metal part of one of the car keys, then touched the clear key fob with the rental car company's information on it.

bit cruelly in = dug into her skin in a harsh or painful way

A: With jagged edges that each typically come to a sharp point. Usually we use it to refer to a serrated knife as opposed to a knife with a smooth edge.

A: Serrated is usually to describe an edge to a knife. Serrated edges are small, sharp repeated patterns.
Jagged can describe an uneven edge. If I knife were to have a jagged edge, it would appear to be chipped, worn down, cracked and used.