I've found that their aura will have a light green afterglow and they will most likely be a pisces born while Jupiter is in retrograde. If you want to make sure, you should also make sure to get a piece of their hair and put it in a potion made with sage, rosemary and thyme as well as a drop of laundry detergent and rat piss (the last step is extra important because it will ward off evil spirits). You should also make sure to ask the typical questions you would ask in this situation, like "Where is your keymaster?", "Do you remember the tree of arcterus grass root?" as well as random chants in Latin. If they look scared, that probably means that they were an eighteenth century peasant who had constant swamp ass and male pattern baldness.