Read The Crabfish (Wikipedia)

"The Crabfish" is a ribald humorous folk song of the English oral tradition. It dates back to the seventeenth century, appearing in Bishop Percy's Folio Manuscript as a song named "The Sea Crabb" based on an earlier tale. The moral of the story is that one should look in the chamber pot before using it.

Owing to the indelicate nature of its theme this ballad was intentionally excluded from Francis James Child's renowned compilation of folk songs The English and Scottish Popular Ballads. The song has a Roud Folk Song Index of 149.