My son sometimes say things like "I am going to get a knife and kill you" or he is going to mess with the fireplace and burn the house down.  Now he says these things when he gets really angry either at me or his sister and he doesn't do anything violent like go around hitting and kicking things or people.  He doesn't mess with the animals and does not "pull the wings off of flys".  He generally is not destructive just sometimes says these things when he gets mad.  He is over it in just a minute and is the laughing little boy that is "normal".  He is very loving towards me {except when he says those things} and hugs and kisses on me all the time.  I can count on one hand the times he has said those things.........should I be worried?  Is it somewhat normal for kids to sometimes say things like that?