When Moshe warns Paraoh about the last plague that God will bring upon Egypt, the smiting of the first born, he tells him: “There shall be a great outcry in the entire land of Egypt - But against all the Children of Yisroel, a dog will not sharpen its tongue, against man or animal, so that you shall know that God will distinguish between Egypt and Yisroel" (Shemos 11: 6-7). The simple meaning of this comment is that while the Egyptian people will be screaming as a result of the plague, Yisroel will be completely tranquil, without even a dog barking at them. However, the Rabbis connect the behavior of the dogs to a seemingly unrelated law. The Torah later, in parshas Mishpatim (Shemos 22: 30), commands the people not to eat flesh that was torn from a “treifa” animal. Rather, the flesh must be thrown to the dog. The Rabbis explain that the flesh is thrown to the dogs as a reward for remaining silent on the night of the plague of the first-born. An understanding of the significance of these dogs will enable us to appreciate the importance of gratitude to them.
Rabbi Avraham, the son of the Rambam, writes that complete silence was needed in the Israelite camp on the night of the final plague. Rabbi Avraham Ibn Ezra explains that the barking would have frightened the Jews. According to Rabbi Shmaryohu Arieli, the Israelites, as slaves, were of lowly spirit. Therefore, they were easily intimidated, and even the barking of a dog would have frightened them. Ibn Ezra writes elsewhere that the generation that came out of Egypt was not ready to enter the Holy Land due to its slave mentality. This mentality was so internalized that even the bark of a dog might have deterred them from proceeding with the redemption process. The Torah's directive to give the treifa to the dog, then, represents an expression of gratitude to the dogs for having aided in this process of redemption. The dogs showed loyalty and gratitude to the Jews, and they, in turn, are owed a debt of gratitude.
Rabbi Bachya ibn Pakudah writes in his Chovos Halevovos that a sense of gratitude is the foundation of one's service of God. The Mechilta on parshas Yisro explains the verse, "I am the Lord your God who took you out of the land of Egypt" with the parable of a king who issued commands to his people only after he did various things for their benefit. The silence of the dogs on the night of the final plague in Egypt served to cultivate a sense of gratitude within the people, so that they could further develop it and use it in serving God. Paraoh and his people, on the other hand, had a complete lack of gratitude for the Jewish people, descendants of Yosef, who had saved them during the years of famine. Rabbi Menachem Kasher, in his Torah Shleimah to parshas Bo, cites midrashim that tell of two magic, silver dogs that were set up by the Egyptians next to Yosef's coffin to prevent Yosef’s family from taking his body with them. The midrash shows that the Egyptians understood the benefit they had derived from Yosef, and, despite that, they subjugated and tortured his descendants. Their sense of ingratitude was so great that they used the image of a dog, the symbol of loyalty, to prevent the Jews from retrieving Yosef's body. Perhaps Moshe, by telling Pharaoh that the dogs would not bark on the night of the final plague, was telling Pharaoh he and his people were on a lower ethical level than those dogs who showed the proper loyalty and gratitude. Mark Twain once observed that if you take a starving dog in out of the rain and feed it and take care of it, that dog will not bite your hand. That, he quipped, is the main difference between a dog and a human being. Although Twain's observation is typically cynical, in the case of Paraoh and the Egyptians it appears to be correct.