In Japanese, the common word for "fool" (idiot, dummy, dolt, blockhead, jackass, etc.) combines the kanji for horse (馬) and deer (鹿), and is pronounced baka (stretch out the first syllable for extra effect). A kirin or Chinese unicorn uses the radical for deer in both of its kanji (麒麟).

Of course, the joke is entirely dependent on an understanding of the Japanese etymology.

Labels: 12 kingdoms, language, poseidon