Yeah, try representing a 3D activity in a 2D comic with an extra dimension for humor, which is often on an imaginary axis ... Maybe it would've looked better if I hadn't insisted that the lines be functions.

Parallel lines always have the same slope and are always the same distance apart.

With curve lines, the distance bewteen them isn't constant -- however, the vertical distance for any x value is always constant. At least, in this example because it's a simple transformation of the function; i.e. B(x) = R(x) + 2.

What about other examples? Well, that's left as an exercise to the reader. Yeah, that's the ticket!