Can a human be vertex?

I see no reason a person couldn't create a circle within themselves, from which to conjure. Not sure why anyone would, but that's neither here nor there. As for random psychics on the street, it's probably best to take what they say with a grain of salt. I don't imagine anyone would naturally have a means to summon things inadvertently from within themselves. I tend to be a skeptic and am inclined to inquire why she assumes that her random chills have anything to do with any sort of spiritual presence. It's best to rule out mundane causes for things before leaping to preternatural conclusions.