"Cracking up" also Means to Laugh

I thought Google images was making my life difficult by returning images of people laughing when I searched for the central phrase "cracking up." I thought this inconvenient idiom would stop me from discovering a meaningful image, but then I found the passage on pages 409 and 410 concerning laughter. In the couse of this passage Paul claims that he never actually laughs when he is happy (Maryrose's observation supports this). A while ago I watched a program on the History Channel called "The History of the Joke." Durring this program the interviewed comedians adressed the nature of laughter. This one elderly comedian said that laughter was a pure and vulnerable state. When one laughs they are exposed in the honest expresion of their emotion. He likened laughter to crying, saying that they two were very similar in this respect.

With this understanding, Paul and Anna's laughter in response to Wili's defense of socialist philosophy followed by Paul's instance that he does not laugh when he is happy makes the phrase "cracking up" and the idiom for laughter much more unified in meaning than I would have first suspected.

In this case Paul and Anna's mirthless laughter in the face of socialistic policy represents a portion of their lives where they are vulnerable. People who laugh when they are happy do so from a more stable place, where they do not fear the exposure of their raw emotions. Maryrose and Willi claim to be a part of this group. In contrast, Paul and Anna's laughter expresses their instability, the cracking up of their own world.

of course after this I could not find an image that I thought adequately expressed this idea but I did find this.

I think there might be some meaning that can be extracted from the fact that this is the traditional representation of theatrical comedy. The lines across the mask serve for cracks and I've always thought the comedy mask looks very close to crying.