Why do calligraphy works write some little scarlet letters?

What you should say is tracking red. It used to be red when practicing calligraphy. Every other page is in red standard script with a thin layer of transparent paper on it. Calligraphers draw red characters, which is called drawing red. In this way, you can practice according to the standard font, and you can feel the correct pen structure and specification. It is a good tool for beginners of calligraphy.