Having already stated the Halachah by someone who strikes an animal (in Pasuk 18), why does the Torah repeat it here?
Why is one Chayav Misah for striking a person even if he does not kill him (since the Torah does not add the word 'Nefesh')?
Rashi: Because the Pasuk is referring to a case where a son strikes his father.
Targum Onkelos and Targum Yonasan: The Pasuk is speaking about where the man killed the victim. 1
Despite the fact that the Torah does not insert 'Nefesh'.
Having already taught us the Din of someone who strikes his father (in Kedoshim Sh'mos, 21:15), why does the Torah repeat it here?
Rashi: The Torah repeats it here next to the Din of Makeh Beheimah, to teach us a. that just as the latter is speaking where the animal is alive, so too does the Din of Makeh Aviv ve'Imo apply only in their lifetime, 1 and b. that just like one is liable for Makeh Beheimah only if he inflicted a wound, so too, is one Chayav for striking one's parent only if he inflicted a wound.
Moshav Zekenim: Above, it discusses striking "Aviv ve'Imo." One might have thought that he is liable only for striking both of them simultaneously. 2 Therefore the Torah writes here "Makeh Adam" to teach that one is liable even if he strikes one of them.
Rashi: In spite of the fact that one is Chayav for cursing them even after they have died. Presumably, this is also how Targum Onkelos and Targum Yonasan will explain the fact that the Torah mentions "Makeh Beheimah", since they explain both Pasuk 18 and the current Pasuk where the striker killed the animal (Refer to 24:21:1:1).
R. Yonason (Sanhedrin 85b) holds that the prefix 'Vav' always includes even one of them unless it says "Yachdav". And there, R. Yoshiyah learns from a Hekesh to cursing parents (about which "Aviv ve'Imo Kilel" (20:9) is superfluous to obligate even one of them! Perhaps R. Yonason learned from here that the prefix 'Vav' always includes even one. (PF)
What is the significance of the comparison of Makeh Adam to Makeh Beheimah?
Rashi #2: Refer to 24:21:3:1.
Bava Kama, 83b: To teach us that, just as Makeh Beheimah pays money, so too does Makeh Adam.
Sanhedrin, 79b: To teach us that, just as Makeh Beheimah is Chayav, irrespective of whether it was Shogeg or Meizid, intentional or unintentional, a downward stroke or an upward stroke - he is always Chayav, 2 so too is Makeh Adam (Aviv ve'Imo) Patur from paying under all circumstances, 3 even be'Shogeg where he is not Chayav Misah.
Sanhedrin, 84b: To teach us that, just as Makeh Beheimah is only Chayav if he inflicts a wound, 4 so too Makeh Adam.
Sanhedrin, 84b: To teach us that, just as Makeh Beheimah a vet is Patur if he inflicts the wound with the intentiopn of healing the animal, so too, is a doctor Patur if he intends to heal his patient. 5
QUESTIONS ON RASHI
Rashi writes that one is liable for striking one's parents only in their lifetime. Why is this different than cursing, for which one is liable even after death?
Moshav Zekenim: Because cursing parents is compared to cursing Hashem, which is applicable at all times.
