THe basis of most joker is that, at the punch line, something disastrous or painful happens to some one. In effect, the unexpexted ending 'frightens' our brain, and we laugh with sounds similar to a chimp warning others of imminent danger. Even though we consciously know that the joke is not areal event, our laugh releases endorphins for self-aesthesis as if the joke was a real event. If it was areal event, we may go into crying mode and the body would also release its endorphins. Crying is often an extension of a laughing bout and is why, in a serious emotinal crisis, such as hearing about a death, a person who cannot mentally accept the death, may begin laughing. When the reality hits, the laughter turn to crying