For Sylvia Branzei, 43, author of such books as Grossology, Animal Grossology, Grossology Begins at Home and Hands-on Grossology, still teaches science and maths to 12 to 14 - year-olds, as she has for the past 20 years, despite selling some 240,000 books since 1995.
The idea for the books first came when she was at home cutting her toe-nails: "I started thinking about the gunk underneath them and it hit me: I should use this for teaching science. So I started writing a book proposal. I was teaching an after-school enrichment course in science and I tried out my ideas there."
She had, she discovered, previously untapped reserves of grossness: "In my home, 'fart' was considered swearing. I practically had to ask my mother if I could use the word in the book."
As she produced page after page on snot, dandruff, eye gunk, tooth tartar and crusty scaly things, her pupils were entranced: "I began to use this stuff when I taught human anatomy and physiology in my regular classes. I had one boy who, went we went on to Newton's Laws of Motion, said to me: 'When are we going to go back to doing real science, you know that gross stuff?'" But some reviewers said it wasn't really science. "In fact it was marketed as a general book, not an educational book at all. Radio interviewers used to say things to me like 'You must be really gross, I bet you pick your nose', and I'd have to turn it round and say 'I'm not gross, I'm not into gross stuff, I'm trying to teach science'.
"But then teachers started buying it and using it. I've had letters from teachers in units for disruptive pupils, I've had letters from prison teachers, I've had letters from college professors, all saying this is such an accessible way to learn science."