What is the purpose of the line in the start function of the leash example?

The purpose of the line in the start function of the leash example is to define the starting point of the line on the canvas. This is essential because establishing a starting point allows for the creation of a visual reference from which all other elements can relate. By positioning the line correctly, it ensures that any subsequent animations, such as the movement of objects or interactions with the mouse, can occur in relation to this defined point. As such, it plays a critical role in setting the framework for how the elements in the animation interact with each other, particularly in determining where the line is anchored at the beginning of the simulation.