2014-09-12
Explanation
The Joke
A group of explorers are searching for a unicorn. One says, "There's no way we'll find the horn of the unicorn. They don't make sense. Every other similar species has two horns or none." Another asks, "What about the narwhal?" The response: "Common misconception. That's not a horn. That's... that's..." The final panel reveals a narwhal with its tusk labeled: "It's a modified tooth!"
The Humor
The joke plays on the real zoological fact that the narwhal's "horn" is not actually a horn at all -- it's a modified elongated canine tooth (a tusk). The explorers are searching for a unicorn and dismissing the idea of a single-horned creature as biologically implausible, since symmetry in horn development is the norm. When someone brings up the narwhal as a counterexample of a real animal with a single "horn," the expert gets flustered and has to admit that the narwhal's protuberance is technically a tooth, not a horn -- which means it doesn't actually disprove their point but also reveals how strange real biology can be. The comic highlights the irony that nature already produced something as bizarre as a "unicorn of the sea," yet people still focus on mythical ones.
References
The narwhal (Monodon monoceros) is an Arctic whale whose males (and some females) grow a single long, spiraling tusk that can reach up to 10 feet. Despite its horn-like appearance, it is indeed a modified upper left canine tooth that grows through the lip.