Contrary to the popular notion that all fairies are good, the Sidhe are "practical" and will do whatever is necessary to achieve their goals, even at the expense of mortals. They speak in riddles and are forever striking bargains, which they stick to, to the letter. The dark Sidhe in particular are mischievous and enjoy playing tricks on humans. When it suits them, the Sidhe can take complete control of mortals. They can heal them, put them to sleep, touch their dreams and steal time from them.