sword
Explanation
The Joke
The comic retells the legend of the Sword in the Stone, where pulling a magical sword from a stone proves one's right to be King of England. A character pulls the sword free and triumphantly declares his right to rule. However, another character immediately challenges this, pointing out that the old method of determining kingship is outdated -- England already has a perfectly good current king through the established system of hereditary monarchy. She then observes that the sword was actually pretty loose, and asks whether anyone else was even trying to pull it out. The final panel reveals that no one else bothered, and she dismisses the feat with "no takesies backsies."
The comic deflates the grand Arthurian myth by applying modern practical thinking to it. The magical trial of the sword in the stone sounds impressive in legend, but when you think about it critically: How hard was it really? Was there competition? And why would pulling a sword out of a rock qualify someone for governance anyway, especially when there is already a functioning (if imperfect) system of government in place?
The Humor
The joke works by puncturing mythological grandeur with mundane logic. The Arthurian legend is one of the most romanticized stories in Western literature, but here it is treated like someone finding a loose item and claiming finders-keepers. The phrase "no takesies backsies" is particularly funny because it reduces an epic moment of destiny to the level of a playground dispute. There is also a sly political commentary: the comic points out that hereditary monarchy is itself a questionable system, but it is still more rational than "whoever pulls a sword from a rock gets to run the country."
References
The comic references the Arthurian legend of the Sword in the Stone, most famously told in Sir Thomas Malory's "Le Morte d'Arthur" (1485) and popularized by T.H. White's "The Once and Future King" (1958) and the 1963 Disney animated film. The concept of legitimate governance being conferred by random feats of strength is also famously mocked in Monty Python and the Holy Grail (1975), where a peasant protests that "strange women lying in ponds distributing swords is no basis for a system of government."