Much of the theory about comedy focuses on the element of surprise. Reversing an audience’s expectations creates humor.
Next, consider tragedy...
...a serious play in which the chief figures, by some peculiarity of character, pass through a series of misfortunes leading to the final catastrophe.
There is also something called a "tragicomedy."
Tragicomedy is a literary genre that blends aspects of both tragic and comic forms. Most often seen in dramatic literature, the term can variously describe either a tragic play which contains enough comic elements to lighten the overall mood or, often, a serious play with a happy ending.
This might be a question of perception rather than a "scientific classification," but while Sally Clark's play Moo is described as a comedy, I find it more a tragicomedy. It is not a serious play with a happy ending by any means, but we might accurately describe it as a tragic play that includes some comic elements.
When Harry and Moo first meet, it is funny certainly in Clark's use of comic timing, that as soon as Moo says she will fall for the first guy who can shoot better than she can, Harry steps into her world and can not only shoot the tin can (as can she), but he also shoots continuously to keep the can suspended in the air.
I tell you what, Sarah. I'll marry the first man who can outshoot me.
When Ditty decides she wants to learn how to shoot, Harry offers to teach her. Ditty's pandering to the macho Harry is also funny:
Now you hold the gun.
Oooooh it's so heavy...
And you—um—put your hand there. Now, don't pull on the trigger.
Now you look down the barrel.
The humor here can be inferred in that Ditty knows so little of guns (or pretends to) when her sister Moo uses one quite often, or in the cliché of the girl who is helpless but for the masculine arms around her.
In this play, Clark includes elements of black humor, which are...
...situations normally thought of as tragic or grave as humorous.
Black humor is seen when Harry gets disgusted with Maude's incessant chatter about having a nose job. When she asks Harry if she needs one, he says no. He tells her that her nose is just fine. But Maude cannot leave it at that. She harps on about her nose until she says:
I think it's ugly. It's a blot upon my face. You know. A real blot.
Throughout the later part of the discussion, Harry has become uncommunicative, simply making a noise:
Maude now turns the conversation around, inferring that Harry has said he does not like her nose:
Have you always thought my nose was ugly?
HARRY gets up, walks over to MAUDE, picks her up and throws her down the stairs.
The audience can see the humor in Harry having had enough of Maude's endless blathering about her nose. However, it is a dark moment when, without comment, he tosses her down the stairs to shut her up.
Patsy is Harry's third wife–and an airhead. As they discuss whether Harry should send Moo a Christmas card, her comments are silly. Harry quietly (at the end of his patience) turns to Patsy, in a serious tone, and asks her:
Did anyone ever put a bullet through your brain, Patsy?
You're a kidder, Harry.
That Moo drops everything to chase after Harry whenever he sends a postcard from some remote island makes the story tragic, as does Harry's decision to help the senile Moo take her life at the play's end.