The objective of the story may have been to justify the subject status of the Canaanites, the descendants of Ham, to the Israelites, the descendants of Shem. The narrative of the curse is replete with difficulties: It is uncertain what the precise nature of Ham's offense is. Verse 22 has been a subject of debate, as to whether it should be taken literally, or as "a euphemism for some act of gross immorality". In verse 25, Noah names Shem and Japheth as the "brethren" of Ham. The Table of Nations presents Canaan and Mizraim (Egypt) among the sons of Ham (10:6). In the Psalms, Egypt is equated with Ham. The treatment of Japheth in verses 26–27 raises questions: Why is YHWH named as the God of Shem, but not of Japheth? What does it mean that God will "enlarge" Japheth? And why will Japheth "dwell in the tents of Shem"? Further difficulties include Ham's being referred to as "the youngest son", when all other lists make him Noah's second son. Biblical scholar Nahum Sarna says that the biggest challenge of the narrative is why Canaan was cursed, rather than Ham, and that the concealed details of the shameful incident bear the same reticence as Reuben's sexual transgression.