Ghouls are partially infected citizens, but who are not completely transformed into zombies (Sometimes Mother Nature has a really good laugh at our expense).
It's really difficult to distinguish between a ghoul and a normal, healthy citizen. As such, a ghoul tends to decimate the ranks of a town if something is not done about it quickly.
I am a ghoul!
In order to survive, you have to keep an eye on the Voracity meter, located at the top right, below your status.
Devour a citizen or consume cold human flesh (in any form) to reduce your Voracity.
How do I become a ghoul?
A citizen can become a ghoul by consuming various suspicious comestibles: Travellers' corpses, meaty bones, human flesh amongst other things... Of course the risks are minimal, but are you willing to risk mutating?
It is possible to use certain products to defend against becoming a ghoul, or to heal oneself once getting into that mess such as the anti-ghoul vaccine!
How do I kill a ghoul?
A ghoul isn't really a zombie and therefore is not immune to death by "natural causes" such as hanging and drug addiction. However, they are immune to thirst and infection, and therefore any related deaths.
As in life, violence is the best solution, and will kill a ghoul instantly. Attention though: aggression costs a lot of and has an increased chance of wounding the victim. Beware of unwarranted violence.
How can ghouls be discovered?
The town register is your biggest ally. You should also keep an eye on the comings and goings of players.
Don't forget that anybody can be transformed into a ghoul! Even the charismatic leader who is calling the shots and giving you good advice.