An uncomfortable conversation is that of humans that no longer resemble humans. Either through magical enhancements or experimentation, ancient artifact or relic use, or pre-fall body transmogrification, some humans are so altered that they no longer resemble humans in the classic sense.
Of course we are all accustomed to various cosmetic changes, but once a person resembles a 12 foot tall mechanical beast it is easy to assume you are in the presence of a "monster".
This is further confused by the fact that some true monsters can talk and imitate human communication, and of course Demons can look both humanoid or monstrous and can converse easily.
The first thing you should do is check how you feel in their presence. If there is a strong sense of danger, or you feel that you need to flee immediately, you are probably in the company of a demon or very powerful monster. If you feel calm, you may be safer, or may just not be very attuned to danger.
Try asking the Human/Monster/Demon what street they grew up on, or the name of their first pet. If they haven't attacked you yet, and additionally if they answer, you should be on the right track.
-Excerpt from "The Adventurers Guide to the Continent"