Don't some people have the rim chopped off. 
Biology not your strong subject then?
Study your Welshman and address such questions to him. When he stops laughing he may even give you the answer.
You know that Wench is a bit on the naive side.
Mind you saying that about Wenchy, I had a girl-friend that thought men used toilet paper when they went for a leak. She had a fit of the giggles, when I explained the shaking process.