Hair Spray Accumulation
This photograph was - quite wrongly - diagnosed as head lice!
In fact it shows a droplet of hair spray which has dried on a single hair forming a perfectly smooth cylinder around it. It has not touched another hair at all.
In this photo you can see a perfect replica of the cuticle of the second hair, here.
What has happened here was that the lady concerned was washing her hair about once a week, and applying hair spray frequently and generously between shampoos. By the end of each week, significant amounts of hair spray had built up on her hair. Fortunately, modern shampoo technology is excellent at removing even a week's accumulation of hair spray, grease and dirt.