I couldn't get your video link to work. I answered you on the Racer Forum about this but you may not have read it. Psammophis have the interesting ability to exude a secretion from their lower jaw. They then proceed to wax themselves down by rubbing their lower jaw along the length of their body. It is thought to protect the snake against dessication. I don't know if this occurs in all species of Psammophis or not but it sounds like this is what your snake is doing. If your snake has mites you'd be able to see them around the eyes, between the scales under the chin, and on your hands after handling. Hope this helps.