Death "Causes" Death?

When I hear this, I wonder does it really happen? I have never seen a person die just because another person had die. Sure I seen it on television or read it in books but I have never seen somebody I know did this. So, I wonder do it really happens? Some classmates in my Death and Dying class have said they have seen it. As I am write this I start to wonder do I really want to know if this can happen. It just be too sad to see a person die like that, but there is that little voice in my head saying to me you still want to know. -__-