dragon
Explanation
This comic features a scene of medieval dragon-fighters preparing for battle.
A warrior argues: "Father, why do we fight dragons with flaming arrows? Fire is their natural element." The father replies "Exactly" -- and then reasons that since fire is their natural element, and they have an internal organ filled with hydrogen (which is how they breathe fire), the dragon is "likely methane, hydrogen, and fats." The conclusion: "From which it follows that it's basically a big ol' bomb and reaching--"
Before he can finish the sentence, the dragon explodes in a massive "BOOM" as an arrow hits it, confirming the theory.
The humor comes from applying real-world chemistry and biology to a fantasy creature. Rather than treating dragons as magically fireproof, the comic reasons that a creature full of flammable gases and fats would actually be extremely vulnerable to fire -- essentially a flying bomb. The irony is that fighting fire with fire, which seems counterintuitive, is actually the perfect strategy. The father doesn't even get to finish explaining before the dragon detonates spectacularly, proving his point.