Useful trick to remember some shapes

In learning unit 1, the following basic outlines are presented

As I looked at these outlines, I realised something: k, g, r and l are all the shape one makes with their their tongue to make the same sound! Try it now, make a k sound and notice how the tongue's shape is very similar for the k outline. I use this trick to distinguish between r and k constantly. Also, in this unit voiced constants are longer than unvoiced (this may be general, but I don't know enough Gregg yet to say so).