When Esau came back from the hunt and saw that Jacob had taken the blessing, he plotted his revenge quietly. The sages, reading the reunion years later in Genesis 33, noticed that Esau said something chilling before the brothers met: "I will not kill Jacob with bow and arrow. I will suck his blood with my mouth."
Then came the moment the Torah describes. "Esau ran to meet him, and embraced him, and fell on his neck, and kissed him, and they wept" (Genesis 33:4). The sages taught that the word vayishakehu, "and he kissed him," should be read as vayishachehu, "and he bit him," letters almost identical, intention nothing alike.
The moment Esau's teeth closed on Jacob's throat, the neck of Jacob hardened into ivory, unyielding as marble. The Song of Songs is the prooftext: "Your neck is as a tower of ivory" (Song of Songs 7:5). Esau's teeth struck the tower and dulled.
When he realized his mouth would not puncture what it had bitten, his kiss turned to rage. He gnashed his teeth in frustration. This, the sages said, is exactly what the Psalmist describes: "The wicked will see it and be grieved; he will gnash with his teeth and melt away" (Psalms 112:10). The tears the Torah mentions were Jacob's tears of pain and Esau's tears of thwarted hunger, weeping for opposite reasons at the same embrace.
The tradition treats the scene as a parable for every embrace Israel would receive in exile. Some embraces are covers for bites. The tower of ivory is the Torah itself, which keeps the teeth from reaching the blood.