I like esoteric humor. The more more obscure the better. This does mean, that when I encounter a joke I don’t get, that I must track down the reference and figure it out.

If you click on the cartoon, it brings up a large version, so you can see the details.

This forced me to check the DVD for Primer out of the library and watch it twice. Once with the director commentary. It didn’t help much. I found a forum with over 8,000 entries discussing the movie:

The SDMB can be a great source of esoteric humor. I remember a few years ago, there was a thread in GQ about topology, with lots of very smart folks (This does not include me; I was just an interested reader.) trying to explain some really complex point about curved space.

Then someone comes in with a one-liner: “My brane hurts.”

I laughed heartily, then paused in awe at the idea that I’m a member of a community that can appreciate topological puns.

I have to apologize for not being able to find the thread or remember the joke’s author.

Another one from here: I don’t recall (and cannot find) the thread topic, but it had gotten into particle physics, and there were jokes. Someone said, “Is that a tau-neutrino in your pocket, or are you just happy to see me?” Geeky, cute, but not really laugh-out-loud. But Dr. Matrix replied with a truly excellent physics joke:

“That’s not a tau-neutrino in my pocket; I’ve got a hadron.”

Still my favorite after many years: “How many theoretical quantum physicists does it take to change a lightbulb? … One. One to hold the ladder, one to turn the bulb, and one to renormalize the wavefunction.”

Well, the Paul Erdős strip plays on the fact that Erdős was a prolific author of mathematical papers, and a frequent collaborator - he had over five hundred co-authors, I believe. The fellow was also enormously well-respected, so the humor derives from:

1.) The idea that, even in the face of otherwise horrifying events (apocalypse, zombies, etc), mathematicians would be thrilled by the possibility of collaborating with Paul Erdős, and;

2.) The implication that Erdős would sign his name to pretty much anything, thus explaining his extraordinary publication record.

The part you’re not getting is the prestige (among mathematicians, anyway) of having an Erdos number as low as possible, preferrably 1—and the fact that, now that he’s dead, it’s still possible to get an Erdos of 2 or 3, but you can’t get a 1 unless he were somehow to… come back from the dead.

So, what’s the absolute geekiest possible response to “the dead walk the earth”? …

The thread with the hadron joke was An expanding universe? Am I expanding? (I found it by Googling for site:straightdope.com universe expanding nose hadron).

And to fully understand the Erdös one, you also have to know that mathematicians (and other academics) keep track of a quantity called the Erdös number, which is a property of a researcher. Paul Erdös himself has an Erdös number of 0, anyone who published a paper with Erdös has a number of 1, anyone who published a paper with someone with 1 (and who doesn’t already have an Erdös number) has a 2, and so on. A low Erdös number is a status symbol of sorts, so all these mathematicians want to get him as a co-author so they can get a coveted 1.

Oh, neat! I see how that works - if you collaborated on a paper with someone who had an Erdos number of six, then your number would be seven. But if your collaborator later does a paper with someone who wrote a paper with Erdos himself, then your collaborator’s Erdos number is now 2, and yours would be 3 - right?