Like st pauli girl, we mentioned the real life consequences of perceived threats. And I felt like a bad mom when I saw the look of terror pass across his face, but it worked!
Our son is 8 now, but at age 5 he said things similar to what you are describing. We DID rush him into a psychologist who assured us that he wasn't becoming a sociopath, but needed better ways to express his anger and frustration.
It has been a continual process. For example, he called his teacher a "mutt" the other day. (Not nearly in the same category as cutting her in half, but it warranted a comment from the teacher to us.)
I am always happy when he just says what he is feeling instead of what he is imagining, but even that doesn't go over well with the school. I was told recently that he was stating he was angry. My reaction was, okaaayyy so? I had to explain to them that verbal expressions of emotion are JUST FINE!!!
