This article examines the use of the so-called kuppû-eel, and particularly its bile, in cuneiform medical prescriptions from ancient Mesopotamia. In therapeutic treatments, the bile of the kuppû was specifically used to treat eye illnesses. Although Wolfram von Soden discussed the eel’s medical uses decades ago, recent scholarship merits a new evaluation of the function of the kuppû-eel in Mesopotamian medicine. By examining how the ancient Mesopotamians encountered and conceptualized this eel, as well as considering how bile and one’s eyes were conceptualized in ancient Mesopotamia, this article identifies conceptual overlaps between the kuppû-eel, bile as a general concept, and illnesses related to the eyes explaining the ancient magico-medical efficacy of the substance. Furthermore, it is proposed that the kuppû can be identified as the so-called Mesopotamian Spiny Eel.