Now, there may be a context in which this could make sense, but if there is one thing xkcd is not good at, it's telling you the context for its little stories. Maybe this is a particularly violent family. Maybe it's a crime fighting baby of some kind. Maybe it's a clever plot to rob the doctor by hiding in a uterus. Who knows? xkcd sure isn't going to tell you. It's just like seeing a single image of a long story, and you have no clue why it's there.
Is it possible that the whole thing is a set up for the final line? Maybe. It's hard to imagine, because the emotion focus climaxes with a gun in the woman's uterus but maybe he just really liked the idea of a doctor, so used to telling women to "push" when giving birth, changing to "pull" when something goes wrong. But why on earth choose this as your idea of a humorous way for it to go wrong? Why something so astonishingly gross and violent?
Randall does not have a very good record when it comes to comics about giving birth. Here's one example, here's another. Notice anything? Yes, they both involve male doctors abusing their relationship with their patients by making them think something horrible is going to happen. Ha, ha. Ha. And yes, like the current comic, they both involve the idea of a baby going back into you once it came out. Ha, haha. Of course, like the current comic, they all are terrible.
Now I'm no doctor, but I'm going to hazard a guess as to why Randall is making lousy comics about birth: He's a dude who is pretty young. Lots of guys his age may already be parents, but he is not. He isn't married. He doesn't have a child and when he does, he won't be the one giving birth to it. They comedy is truth and that to make fun of something you have to really know it, and I think that's why a twenty-something male really shouldn't be making comics about birth.
OK, I'll change that - I'm not going to tell people what they can or can't write about. I'm just going to say that for a twenty-something guy to be making these comics, he's going to have a harder time with it.
It is possible to make something good on the topic. Some people have been linking to a certain fetus-themed PFSC comic. I don't think this comic is as funny as the Onion article I link to below - some cuddlefish is going to say it isn't even as funny as the xkcd, but they are wrong - but it's still funny, partly because of how surreal it is ("the McDonald's inside you"), and partly because of how both characters take the events in stride, so calmly.
Now, granted, in this particular case, showing us the gun may have meant showing us the woman's uterus. Which I would have disliked even more. Is that a good argument against what I've written? No, it's a good argument about not setting your comic in a freakin uterus.
Let's get back to talking about context. Here's an old Onion article that bears a remarkable resemblance to today's comic: Nation Shocked by Pre-Natal Shooting. It's worth reading all of. Why is it funny when today's xkcd isn't? Both use the image of a fetus with a gun committing or attempting to commit a violent crime. The key difference is that the Onion has a good reason for this: It's a darkly comic piece parodying the violence among youth in America, particularly violent crimes committed by very very young children. The tone of the article makes clear that it is a parody of real stories that had only slightly older children involved. There's still an inherently icky feeling about it, but it serves a purpose. This comic's purpose seems to just be...well, I can't tell what it is.
OK, I think it's time I head on over into the forums and see what they have to say. Perhaps they can enlighten me. Perhaps they can enrage me. It'll be fun I am sure.
Maybe you noticed because you were reading the comic and saw it happen? The doctor is clearly using a magic string that disappears when you look too closely at it. That must be it, otherwise the implication is that Randall forgot to finish the drawing for some reason. That would just be silly! he is a professional.
OK this is a comment I really like - admitting the comic makes no sense and suggesting at least a pun that he could have used.
....and that's all I care about. Mostly people who are complaining that this comic makes no sense.
WELL, I guess that is it then! No one can explain this comic.
One final word: Sometimes, xkcd is good. Sometimes its bad. It can be bad for a variety of reasons. Sometimes the joke is ok but it just makes you feel weird because of the subject matter. Sometimes the subject is perfectly inoffensive but the joke isn't actually funny or doesn't make sense. And sometimes, you just can't tell what the joke is. This is a case of all of them - the strange, off-putting subject matter makes you feel gross (i hope) but the payoff is zero; there's no good reason we had to read all that.