Dr. Phoenix
What tone of voice makes it flirting?
If you pronounce certain words in a different way. You may not even notice, but your partner definetely will. The one talking is perhaps not able to notice the difference, as we have already found out that the line between flirting and being friendly is very thin. It's the same with your voice.
We humans were made for without even realizing it, noticing such little signs and therefore know wether one is flirting with you or just being friendly. And because this signs are really hard to read and to see, funny and sometimes even terrible mistakes are likely to happen. *nods*
And as B.u.n.i.e. already said, I also believe that the topic you discuss is also very important, when I like someone I would never talk about Freud's interpretation of dreams, but of sports and sweat.
sweatdrop