Witchaven villagers used to be human until the Sea slugs came and invaded. They now have yellowish skin, and speak strange things. They also have reddish eyes. Apparently, they have a very low tolerance level on heat, like the fishermen on the Fishing Platform and will collapse upon contact with it. You have to avoid the villagers in Kennith's Concerns in the underground mine below Witchaven and also knock the last two batches of villagers out by putting Rubium in the steam vents. After the quest is over they will leave the mines. They are also encountered outside and in the Slug Citadel, and can bind the player and summon Risen knights if not knocked out. After Salt in the Wound, they become normal again.
Oddly, examining a villager from Kennith's Concerns can reveal them to be female despite having a male appearance. In addition, the female villagers you lure into the church during the quest turn into males after they get locked in.