Hwang Jini's riddle is a play on Hanja
Korea's most famous gisaeng was a skilled poet and wordsmith of 16th Century Korea. According to the wikipedia summary below, her riddle is one of her most well known written works.
Hwang Jinis Riddle:
Hwang Jini was known for her intellect and wit. Her most famous written work was the Jeomiligu Idubulchool ( 점일이구 이두불출/點 一 二 口 牛 頭 不出 ). She gave the riddle to any man who wanted to be her lover and she waited for many years until one man came and solved the riddle. The answer to the riddle; however, was in the title. When combining the variations in the title the first part Jeomiligu ( 점일이구/點 一 二 口 ) created the Chinese character meaning spoken word (言 ) and the second part Idubulchoo; ( 이두불출/ 牛 頭 不出 ) created the Chinese character meaning day (午 ). When you combine both words together it creates the Chinese character meaning consent (許 ). The reason being that whoever solved her riddle she would allow him to come into her house and share a bed with him. This being one of her most famous written works shows her wit and intellect that most women during the time were not able to share with the rest of the world.[5]
https://en.wikipedia.org/wiki/Hwang_Jini
I could not have solved this riddle without the explanation given above even though the hanja (traditional Chinese) characters are simple ones that can be recognized from a relatively limited vocabulary. I had no idea that the riddle explained the creation of the character for consent or permission in hanja. ( 許 허 heo ) This is so humorous to come from a gisaeng and is a reflection of her social status, in a position to refuse suitors.
점일이구/點 一 二 口 means point or dot, one plus two (3 horizontal strokes) and then goo representing the mouth. This forms the the traditional Chinese radical for speech, ( 言 ). The second part of the eight character riddle ( 이두불출/ 牛 頭 不出 ) has a glitch in it, because 牛 is 우 as in beef or cow, not 이 but it's not the meaning but the stroke in the hanja character that is important for the riddle. All that is needed to convert 牛 to 午 is to retract the cow's head in the pictorial character. This is the exact meaning of 頭 不出. ( 두불출 ). There is more than one double entendre.
The English translations of the poetry pieces on the wikipedia entry on Hwang Jini are challenging as well.