Proverbs 26:11 is the direct source of the proverb about a dog returning to its vomit — applied here to apostates returning to their old sinful ways.

Numbers 14:4 depicts Israel wanting to return to Egypt — a pattern of apostasy mirrored by those who return to their former sinful ways.

In Deuteronomy 14:8, the pig is declared unclean — the OT basis for the sow imagery used here for defilement.

Matthew 7:6 warns against throwing pearls before pigs and dogs — the same unclean animals used here for false teachers.

Luke 8:13 describes those who believe temporarily then fall away — parallels the return to sin after washing in Peter.

Philippians 3:19 describes enemies whose god is their belly and end is destruction — parallels the destructive path of false teachers.

Deuteronomy 23:18 uses 'dog' as a term for an unclean person, reinforcing the negative symbolism of the dog in Peter's proverb.

Proverbs 11:22 uses the pig as a symbol of incongruity — similar to the sow returning to mire after washing.