What is the meaning of the word "Eifo"?
Rashi #1 and Rashbam: It is an expression that has no clear translation. 1
Seforno: 'Eifo' which ends with an 'Alef' (as it does here) means 'if so.' 2
Malbim: To where did he disappear?
What did Yitzchak mean when he declared, "I ate from everything!"?
Rashi: 'I tasted whatever I wanted to taste in what he brought me, 1 and he realized that his beloved son Esav had lost the Berachos forever to Yaakov and his descendents.
Bava Basra 17a: Refer to 24:1:2:6 - and the same applies here with regard to Yitzchak.
Oznayim la'Torah: Esav asked Yitzchak to eat at least something from his venison as well, to which Yitzchak answered that he had already eaten the Afikoman, after which it is forbidden to eat. 2
Like the Manna.
Oznayim la'Torah - Perhaps we can expound that the word "mi'Kol" (in the phrase "va'Ochal mi'Kol") is the acronym of 'Matzah k'Zayis la'Acharonah.' Refer to 27:17:1:1 and the note there. And on Pasuk 27:35, citing R. Yosef Chayim Sonnenfeld, he points out that the Gematriya of "b'Mirmah" is equal to that of 'Afikoman,' to teach us that, since he had already eaten the Afikoman, he would not be able to eat from his venison, and that his Berachah would therefore not be complete.
What is the significance of the phrase "Gam Baruch Yih'yeh!"
Rashi: So that you one should not for one moment think that Yaakov only received the Berachos through trickery - therefore Yitzchak declared (even in front of Esav) that he verified the blessings that he gave him. 1
Bearing in mind that Yaakov tricked Yitzchak into giving him the Berachos, why did he affirm the Berachos instead of cursing him?
Seforno: He realized that the Berachos that he gave Yaakov had taken effect. 1
Rashbam: (a) Because he hurried to serve him; (b) Because he knew that he acted upon Rivkah's instructions, and that she evidently knew which of the two was worthy of the Berachos.
Ramban #1: Yitzchak was not affirming the Berachos. What he meant to say was 'Who was the one who was able to trick me into blessing him? I know that he was already blessed.
Rashi (to 27:36): When Esav complained that Yaakov must have been called by that name because this was the second time he had tricked him, Yitzchak asked him what he meant. And when he explained how he (Yaakov) had purchased the Bechorah from him, Yitzchak exclaimed, And I was afraid over this!? 2 In that case, I blessed the right person 3 - "Gam Baruch Yihyeh!"' 4
Rashi: Refer to 27:35:1:1.
Ramban #2: The Berachah is effective Bal Korchi (against my will), for I know via Ru'ach ha'Kodesh that it took effect.
Ohr ha'Chayim: He was stunned at the trickery, unaware of who it was; he realized that he just cursed anyone who will curse him. He then realized that it was Yaakov, and blessed him, for he had smelled his garments, 5 and [now] knew the difference between him and Esav, and affirmed the Berachos.
Like the Gemara relates (Berachos 34b) regarding the Berachos of R. Chanina ben Dosa, who knew that, if they came out of his mouth fluently, they had been accepted.
Lev Eliyahu (Bereishis, p. 89): Yitzchak intended that Esav receive wealth, and support Yaakov financially, like Yisachar and Zevulun. When he heard that Esav sold the Bechorah for lentils, he knew that one cannot rely on him to support Yaakov, for he is not concerned for the world to come.
In any event, from the day of his birth HaSh-m considered Yaakov the Bechor (Refer to 25:26:2:1*). (According to this answer, Pesukim 33-35 are out of order.)
Perhaps this means that he smelled Gan Eden, and understood that HaSh-m wanted him to bless him.
What is the significance of "ha'Tzad Tzayid"?
Ha'amek Davar: Ru'ach ha'Kodesh caused him to say this. He was Tzad (trapped) Esav, who is called "Ish Tzayid."
QUESTIONS ON RASHI
Rashi writes that Yitzchak trembled. Why did Esav's response make him tremble?
Rashi: He saw Gehinom open underneath him. 1
Rashi (to 27:36): Because he thought that he had upset the order of lineage by blessing the younger brother before the older one. 2
Rashbam: If it was Esav who just entered, 3 then (before it was Yaakov;) how did he have hair on his neck?
Targum Yonasan: He trembled when he heard that it was Esav and the dish that he brought him smelt of Gehinom. 4
Ramban: He was shocked to discover that he had blessed Yaakov and not Esav as he had thought. 5
Malbim: There were many wonders, which showed that HaSh-m caused this. (a) It is not known who it was; (b) To where did he disappear? (c) How was he able to catch an animal so quickly? No one knows as well as you! (d) How did he know to bring to me? I did not tell him! (e) I ate everything (even though I usually cannot eat very much) - or, like Chazal say, I tasted in it all worldly delights. (f) He came before you; (g) I blessed him without realizing from his voice that it is someone else.
Oznayim la'Torah: In keeping with the Gemara in Yevamos 109b, which states that a judge who judges should see Gehinom open beneath him - a warning of what awaits him in the event that he is guilty of perversion of justice. Consequently, now that Yitzchak was about to pervert justice by giving the Rasha Esav the Berachah of a Tzadik, he saw Gehinom open underneath him, and Esav's true identity struck him.
A fact of which he had no doubts.
Rashi writes: "va'Yecherad - an expression of bewilderment." Why not explain simply as fear?
Gur Aryeh: Yitzchak did not regret having blessed Yaakov. Rather he was astonished, which also causes trembling.
Rashi writes: "Homiletically, he saw Gehinom opened...." Why does Rashi add the Midrash?
Gur Aryeh: According to the Midrash, we can translate 'va'Yecherad' as fear, as it is normally translated.
Rashi writes: "Yitzchak saw Gehinom open beneath him." Beneath whom?
Gur Aryeh: [Not below himself, but] below Esav 1 - in contrast to Yaakov who had entered with the fragrance of Gan Eden.
Rashi writes: "Eifo is an independent exclamation... Ayeh Foh? (lit. where is here?)" What does Rashi mean?
Gur Aryeh: "Eifo" is a contraction of Ayeh Foh, but this can be interpreted in various ways depending on context. In this case, it means 'where is [he who was just] here?' In 43:11, it means '[I must find] where is [a solution] here.'