What is the significance of the words, "va'Yifen Pharaoh ... "?
Targum Yonasan It means that Pharaoh defecated 1 and went home.
Oznayim la'Torah: When Pharaoh saw the devastation 2 that Makas Dam caused in front of his eyes, overcome with fear that he might be unable to resist any longer and capitulate - and lose his Jewish slaves, he quickly turned around and returned to his palace. 3
Out of fear. See Na'ar Yonasan.
Refer to 7:23:1.1:1**.
Perhaps he also felt embarrassed to stand in front of Moshe and Aharon stripped of all his dignity and self-respect.
What are the implications of "Gam la'Zos"?
Rashi, Ramban #1 and Rashbam: Pharaoh took no notice either of the miracle of the staff, 1 or of that of the water. 2
Ramban #2: He took notice neither of the sign of the staff, nor even of the plague of the water turning into blood - which ought to have served as a warning that Hashem had now begun to strike him.
Seforno: He was not even impressed by the fact that his magicians were unable to perform what Moshe and Aharon had performed. 3
Rashbam: When he had already hardened his heart.
See also Rashbam to 7:28. The Oznayim la'Torah explains that, as opposed to the miracle of the staff, which - although it demonstrated Moshe and Aharon's superiority over the Egyptian magicians, it caused him no loss; the miracle of the blood created devastation - inasmuch as it left the entire country without water and without fish for an unknown period of time, and Pharaoh's self-acclaimed 'divine power' ("Li Ye'ori, va'Ani Asisini" (Yechezkel 29:3)) was publicly ridiculed - refer to 7:21:1:2*.
QUESTIONS ON RASHI
Rashi writes: "'To this one either' - [I.e., He paid heed neither] to the wonder of the staff turning into a Tanin, nor to this one, of blood." Why is this phrase added only here, and not by any of the other Makos?
Gur Aryeh: The two events were fundamentally different - the staff was a Mofes (a wonder), whereas the blood was a Makah. The Torah tells us that Pharaoh heeded neither. Everything that would follow would be of one type - Makos.