Huck is still a child, he needs to experience what kids do. like messing around, so him taking and killing that snake and putting it by Jim's head was a "playful" intention. It was not a smart intention, and quite frankly its not really all that funny, poor Jim. But all is well now.
I also can see why they would think talking about hank bunker would stir up some paranoia about him coming to haunt them, but it's just paranoia and I thinks it kind of funny that Jim would think that, but I guess it makes sense, because obviously Huck goes along with it too.
But what I want to know is, how trustworthy is this "Mrs. loftis" is, and if she would say anything. Honestly, I think it is a safe move for Huck to create a new identity, but at the same time I don't think he completely trusts her; because if he did I think he would of told her everything. But my guess is that she will eventually find out, hmm...but who knows I guess.