They can be things we fear the most in life. As in things we would never really like to see happen. Thus when we get such thoughts, and if we are the person in the thought carrying out the act, it can scare people. Now one method some people use is a simple elastic band. A loose one, not a tight one as we don't want to cut off the blood flow. Hang it on the wrist. You begin to get these thought let it sling. Works for some people. And for others who think it is a silly idea it is used in pych hospitals. They do hand them out to patients. So there must be something in it. No harm in giving it a go.