Jagged Edge Tearing Tool
The Jagged Edge Tearing Tool is used to help guide the tearing of paper. Surprisingly, it is fairly difficult to tear a piece of paper in a straight line, and this tool allows you to tear a piece of paper in a way that creates a straight tear. The tool has two different edges depending on the amount of jaggedness that you are looking for in your tear.
Here is an example of a page where I have used the tool to make tears for the side edge borders of the spread: