onions-2
Explanation
This comic is a parody of melodramatic children's adventure stories. A child announces to their parent that they stole something (apparently an onion or similar item from a garden), and the parent's reaction escalates dramatically: "That's a adventure garden!" suggesting it's something far more significant than it appears.
The comic then cuts to an absurdly dramatic scene where someone yells "Run boy, run! I will block the avalanche with my body!" -- presenting a wildly over-the-top heroic sacrifice scenario. The final panel, set "20 years later," shows the now-adult child being asked "Why do you cry when you cut onions?" -- connecting back to the opening. The implication is that the character cries when cutting onions not because of the chemical irritant (syn-propanethial-S-oxide) but because of the traumatic childhood memory associated with onions.
The humor works by taking the mundane, universal experience of crying while cutting onions -- which has a simple chemical explanation -- and constructing an elaborate, melodramatic backstory to explain it emotionally instead. It parodies the trope in fiction where a character's seemingly ordinary quirk is revealed to have deep, traumatic origins. The joke is in the absurd contrast between the simple biological reality and the overwrought narrative explanation.