SF, I see you didn't bother to click the link I gave you. I even made sure it was a .uk just for you.
The highlights, though:
- By sharing toys
- Oral sex, especially if one is having their period
- Digital insertion, especially if there are long fingernails and an open wound
- Gonorrheoa, chlamydia, herpes, HPV (which can lead to cervical cancer) and sphyillis can all be spread through oral sex.
Just because you can't imagine it doesn't mean that there's not a risk factor. There's a very real one.