werewolf
Explanation
The Joke
A father is telling his child a bedtime story, setting up the classic werewolf premise: "You know the stories where the moon rises and werewolves uncontrollably turn into big hairy monsters everyone worries about?" The child responds with an eager "Yeah?" expecting a scary tale. The father then delivers the punchline: "It's basically that, only the moon gets stuck." The final panel reveals the father sitting on the bed with the caption: "Dad gave me a short talk on puberty."
The comic reframes puberty as a werewolf transformation. Instead of a temporary monthly change triggered by the full moon, puberty is presented as though the moon got "stuck" -- meaning the monstrous transformation into a big, hairy creature is permanent. The father is using the werewolf myth as an analogy to explain to his child that they will permanently become a large, hairy, somewhat uncontrollable version of themselves.
The Humor
The humor works on multiple levels. First, there is the absurdity of using a horror movie trope to explain a normal biological process. Second, the description of werewolves -- "big hairy monsters everyone worries about" -- maps surprisingly well onto the experience of puberty, where adolescents grow larger, hairier, and become a source of worry for parents. The phrase "the moon gets stuck" is a brilliantly concise way to say "it's like a werewolf transformation, except it never reverses." It is the kind of unhelpful-yet-accurate explanation that a lazy or awkward dad might actually give.