Man’s best friend[1]
ויאמר לו יקוק לכן כל-הרג קין שבעתים יקם וישם יקוק לקין אות לבלתי הכות-אתו כל-מצאו
Hashem said to him: “Therefore, anyone who kills Cain will be avenged sevenfold.” Hashem placed a sign for Cain, so that no one who finds him will harm him[2]
Hashem severely punished Cain for murdering his brother. In response, Cain stated that his sin was too great to bear[3] He admitted the error of his ways. In response, Hashem promised justice against anyone who harms Cain. To assuage his fears from foreign attackers, the Torah says that Hashem gave Cain a “sign”. We aren’t told what this is. One opinion of our Sages[4] is that Hashem gave Cain a dog. This seemingly was meant to bea guard dog, which would fight off any foe. The problem is, it’s hard to fit this into the verse. How could placing a sign mean a dog? It should have said that Hashem gave Cain protection, or something similar.