there-and-back-again
Explanation
The Joke
The comic shows a scene from The Hobbit/Lord of the Rings: characters in Mirkwood Forest, with one saying "This doesn't seem right, Bilbo" and another replying "Quit complaining -- getting eaten by spiders does?" The caption below reads: "Getting through Mirkwood Forest was a lot easier once we started using chemical defoliants."
The Humor
The joke applies a modern military solution -- chemical defoliants, most famously Agent Orange used during the Vietnam War -- to a fantasy problem from Tolkien's universe. In The Hobbit, the company of dwarves (and Bilbo) must traverse the dark, dangerous Mirkwood Forest full of giant spiders and other threats. The comic imagines them taking the pragmatic but horrifying shortcut of simply destroying the forest with herbicides rather than bravely fighting through it. The humor comes from the jarring collision of cozy fantasy adventure with brutal modern warfare tactics, and the implied commentary that real-world "solutions" to difficult journeys tend to be far more destructive than heroic.
References
The title "There and Back Again" is the subtitle of J.R.R. Tolkien's "The Hobbit" (1937). Mirkwood Forest is a major obstacle in the story where the company encounters giant spiders. Chemical defoliants, particularly Agent Orange, were infamously used by the United States military during the Vietnam War to strip forest cover.