So, I'm not a scientist (technically), but I have to assume this assessment works in my pro-double-dip favor, correct?
"Regular oral bacteria should not cause any problem, in this case," Tetro confirmed.
"But bacteria is not the only thing that can be transferred via double dipping," Tetro said, promptly hoisting me on my own petard. "Especially if someone is sick with a virus. This can be a twofold problem: You're exposing your body to something it might not be familiar with, so there could be an immune response. And if it happens to be a pathogen, such as the flu, cold viruses, or herpes viruses, this could potentially lead to an infection."
This is what scientists and science-enthusiasts alike refer to as the "minimal infective dose." Basically, you have to be exposed to certain number of the bug in order for you to get sick. In the bacterial sense, it's tens of hundreds of thousands of microbes. So that can't happen via dip, unless someone literally spits in it. But with viruses, it could be as little as one microbe, according to Tetro -- which unfortunately can be spread via dip. And even scarier, people can be contagious with viruses without even showing symptoms.