Metallurgy
Metallurgy
[Cueball and Megan are in a weapon store talking to a bearded salesman wearing a hat.]
[Salesman holds up a sword.] Salesman: This sword was forged from a fallen star. Antimony impurities make the blade surpassingly brittle and weak .
[Salesman holds up a dagger.] Salesman: And this dagger is made of metal from a far-off kingdom. It glows blue. Off-panel: When orcs are near?
Salesman: No, always. Radiation from the Actinium content. Megan: ...Does it have Eldritch powers?
Salesman: It gives the wearer +2 to cancer risk. Cueball: I think we should find another shop.

The comic explains how weapons would really behave if they were made out of unusual materials. In fantasy stories, using unusual materials for weapons traditionally makes the weapons more powerful and cooler despite limited explanation for exactly why materials of extraterrestrial origin are so superior to their earthen counterparts. The salesman in the comic is Beret Guy which appears with a beard for only this comic.
The first panel is a reference to a fairly common fantasy trope: the use of iron meteorites for making weapons and armour (for example the sword "Brisingr" of the Inheritance series, "Anglachel" in the Tolkien Legendarium or the panserbjørns' armour in Pullman's Northern Lights). The quality of such metal can be rather hit-and-miss. On one hand, iron from meteorites was often mixed with "terrestrial" iron in the early stages of human development to create relatively high quality steel for swords. Undeveloped metalworking techniques at the time meant that extraterrestrial metal was often more refined and plentiful than man-made metal ingots. With that in mind, however, research has shown that meteorites have an abundance of the chemical element Antimony (Sb) which by itself is a very brittle metal and therefore swords forged from metals harvested from meteorites may not be as strong as lore would have one think.
The second panel is a reference to stories set in Middle-earth where swords such as Orcrist, Glamdring or Sting (the swords of Thorin, Gandalf and Bilbo/Frodo) glow blue when Orcs are near. The dagger in question, though, glows because of the radioactive properties of Actinium (Ac) which is also highly toxic. Definitely not a dagger you would want to carry around for your every day battles.
The word "Eldritch" in the third panel means sinister, ghostly, or magical.
The fourth panel mentions that the weapon gives a +2 to a player's attribute. This is a reference to role-playing games in which it is common to find items that are able to improve one's character by increasing desirable attributes.  In this case, however, +2 to cancer risk, a consequence of the dagger's radioactivity, would definitely not be considered a desirable attribute to increase. This would hit harder on Randall due to his now-wife being diagnosed with breast cancer.
In the title text, the salesman tries to sell Cueball another meteoric blade, this one made from a carbonaceous chondrite . Carbonaceous chondrites are rocky meteors that generally don't contain a lot of metallic iron. The salesman is either stating that the blade is simply a bunch of nonferrous meteor fragments glued together in the shape of a sword, or stating that the iron he got out of the meteor is so full of impurities that it may as well be gravel. However, because it's made of extraterrestrial material he seems confident he'll still be able to sell it on novelty value alone.
[Cueball and Megan are in a weapon store talking to a bearded salesman wearing a hat.]
[Salesman holds up a sword.] Salesman: This sword was forged from a fallen star. Antimony impurities make the blade surpassingly brittle and weak .
[Salesman holds up a dagger.] Salesman: And this dagger is made of metal from a far-off kingdom. It glows blue. Off-panel: When orcs are near?
Salesman: No, always. Radiation from the Actinium content. Megan: ...Does it have Eldritch powers?
Salesman: It gives the wearer +2 to cancer risk. Cueball: I think we should find another shop.
