I’m no lawyer, and I don’t have access to everyone’s favorite friend (Google) right now, so I’m just going to say what I remember the law was.
A death threat can be prosecuted if the prosecution can prove that the person is able to carry out the threat (and has motive I believe).
For example: if people reply to me in the WB thread saying “I’m gonna stab you if you get another white bag”. Do they have motive? Sort of… if you don’t understand the joke context. Can a prosecutor prove they had the means to kill me? No. The person “threatening” me doesn’t know where I live (I hope ), and they can’t prove that the person had a knife to stab me with. In addition, if the person making the “threat” happens to have no arms, they do not have the means to stab the victim and thus cannot be prosecuted.
Now if you sent someone a picture of their house/address with you holding a knife saying “I’m gonna stab you little timmy”, that could probably be prosecuted.
(Again I might have gotten something wrong here, but I can’t double check. I know the “no arms” thing is true though.)