Dogs were domesticated very early and were used for hunting and as watchdogs in the ancient world. In Egypt as early as 4000 B.C. people made pottery images that indicate that sleek fast hunting dogs were bred which looked like the modern greyhound. From Babylonian sculpture we know that around 2500 B.C. large hunting dogs that looked like the modern bull-mastiff were kept by people in the Mesopotamian civilizations.

Among the Jews however while dogs were kept mainly as watch-dogs they were held in contempt and left to feed themselves by scavenging. This habit of scavenging and the fact that dogs were possibly associated with some Egyptian gods meant that dogs were seen as very unclean animals by the Jews. The dog found in Jewish settlements in Bible times was probably the pariah dog Canis familiaris putiatini which looked something like a small light brown Alsatian or German shepherd. This type of dog in its wild and domesticated forms is found all over the Middle East and on the mainland coasts of South and Southeast Asia (where it is known as the crab-eating dog). The Australian dingo is also very similar.

Small pet dogs were kept in homes in the Greek and Roman civilizations by gentiles but not by Jews. This is probably the type of dog referred to by the Greek word kunarion in Matthew 15:26 and Mark 7:27.

[Sarah Ruden (2021, p. 27), who translates kunarion as “little doggy,” says the following: “In the entire Greek Bible, only [these two passages] use this diminutive (kunarion) of the word for ‘dog,’ a rare and largely comical word. This word choice weakens the usual sense of dogs as dirty and uncivilized and excluded from the home, much less from the table that symbolized God’s providential bounty.”]

As mentioned above dogs were held in contempt as unclean. To call someone a dog was therefore very derogatory and to refer to someone as a “dead dog” was even more so. Israelites viewed dogs as second only to pigs as unclean animals. Dogs as scavengers around the villages ate anything from household refuse to animal carcasses and human excreta. They even ate human corpses that lay unburied after battles. Furthermore the dog was possibly one of the symbols of the Egyptian god Anubis (although many modern scholars believe the symbol to be the jackal).

With all of the above in mind it is understandable that dying and then being eaten by unclean dogs was seen as the worst of all possible fates.

In the first century A.D. gentiles were considered to be unclean and were referred to by Jews in a derogatory way as “dogs.” There is therefore strong irony in the expression in Philippians 3:2 where Judaizing Christians are referred to as dogs.

One additional connotation associated with dogs in the Bible is sexual perversion and promiscuity a connotation probably arising from the fact that sexually aroused male dogs do not always differentiate between sexes as they seek to mate and the fact that dogs of both sexes mate repeatedly with different partners.

Source: All Creatures Great and Small: Living things in the Bible (UBS Helps for Translators)