Kayla raised her hand, "A boggart is a shape shifter that takes on the form of what we fear the most, so I would say that it feeds on our fears. If a person didn't fear anything then they would unlikely to be able to take shape into anything." She thought about what the other's were saying about Dementor's. "A dementor senses and feeds off a person's positive emotions and sucks the goodness out, leaving them reliving their worst memories. So they don't necessarily feed off our fear but off our positive emotions."