Interpreting why in "Isaac trembled very exceedingly," Rabbi Johanan observed that it was surely unusual for a man who has two sons to tremble when one goes out and the other comes in. Rabbi Johanan taught that Isaac trembled because when Esau came in, Gehenna came in with him. Rabbi Aha said that the walls of the house began to seethe from the heat of Gehenna. Hence asks, "who then (, "eifo")?" for Isaac asked who would be roast ("leafot") in Gehenna, him or Jacob?