My boyfriend has a morbid sense of humor..?

I don't really know how to deal with it. He has this pocket knife that he carries around, and sometimes he'll just pull it out, and act like he's gonna stab me, but then he's like "nah, I wouldn't do that." I don't know, the whole knife thing just scares me. And he finds choking amusing. Like, I was sitting on him, and he took his shirt off, made it into a rope-type thing, and put it around the back of my neck, and then twisted it, and I couldn't breathe for like, 2.5 seconds. Now, I admit, I find some pretty morbid stuff amusing too, but I've never.. done what he does. Like.. I laugh when people die in horror movies-- but thats the extent it goes to. I don't know, but how can I deal with it? Do I just act like I..like it?