Constantine
In short, I have an evil hand, which I ultimately have no control over. Some years ago, when I was mortal, a vampire would stop at nothing to get a certain relic, which I held in my hand. He threw a well aimed scythe, and relieved me of the hand that held the scroll. The company I worked for harvested a replacement hand, after a time, and keeping to the short version, this hand knows it does not belong to me.