Two Enemies

כי תצא למלחמה על איביך ונתנו ה אלקיך בידך ושבית שביו

The possuk first identifies the enemies in the plural form and then changes to the singular form, ונתנו, why the switch? (The Baal HaTurim says איביך in missing a י but that is not how we have it, see Minchas Shai.) The Kli Yakar explains that there are two enemies, there is the enemy that the war is being waged against, the external enemy and then there is the internal enemy, the fight with the yetzer harah. These two approaches carry over into the next pessukim. The parsha of יפת תואר on the first level of the general war against the enemy speaks of a situation of לא דברה תורה אלא כנגד יצר הרע. On the level of a personal fight the Or HaChayim explains the יפת תואר refers to trapping the sparks of kedusha that one elevates by abstaining from sin.

Killed Not As A Consequence

 Regarding 4 death penalties the Torah adds ישמעו ויראו. Regarding the ben sorer u'moreh (21:20,) the עד זומם in Shoftim (19:20) the zaken mamreh (17:13) and a מסית in Reah (13:11.) The Gra points out that is due to the law that is by these four cases Beis Din announces the reason why the death penalty is being carried out (see Sanhedrin 89a, the Rambam generally rules it means to carry out the death penalty on the holiday when all are present but for adim zommimim he rules that Beis Din sends out letters, see Aeuch Hashulchan C.M. 38:7.) Why are these four sins singled out that for a public demonstration to stamp out these sins? 

The Ramban explains the ben sorer u'moreh did not do anything to deserve of the death penalty and he is killed " to discipline the public so that others will not stumble... as a protective boundary, so that their death serves as a remedy for others." The death penalty is administered purely in order to be a deterrent for sin not as a consequence of his actions. The Ramban continues that the same holds true for the zaken mamreh who is killed merely to stamp out disputes with the courts and the adem zommimim who are killed despite having not actually affected anything through their testimony and the מסית who is killed merely for encouraging false faith even if his efforts are unsuccessful. That is why it is these 4 examples that Beis Din announces the sin for it in the context of these 4 examples that Beis Din punishes the victim not as a punishment for the action but to prevent an outbreak of greater problems. One killed for their sin does not the news paraded around for their is no concern for a general breakdown in society but when the entire purpose of the punishment is למען ישמעו ויראו then it is a requirement. 

The Rambam (Adut 20:4) says עדים זוממים do not need התראה לפי שאין בהם מעשה . The Raavad asks that there are other cases of sins without an action and they still need התראה? Rav Moshe Soloveitchik explains that the Rambam means that the adim are not killed due to their "action" of giving testimony as the Ramban above noted, but are killed due to the label of עד זומם being given to them (שם בגברא.) In that case there is no need for an active warning. Rav Soloveitchik (his Son) points out that the same argument is followed in halacha for the other above instances of זקן ממרא, בן סורר ומורה, מסית as well that they do not need a warning (see Rashi Sanhedrin 71a, Sanhedrin 66, Mamrin 3:8.) The reason being the same, they are not being killed due to their actions but the action creates a status on the person of being eligible for the death penalty. A warning is needed to define an action, but not to establish a status on the individual. 

(The explanation for עד זומם is צ"ע to fit with the Gemarah BK 4b that lists עדים זוממים as a mazik indicating they are punished for the act of causing harm, but see Tosfos there.)

Animals of Condemned City

The Gemarah Chullin (140a) has a drasha to exclude the birds of an עיר הנידחת to be used for the shechita bird of a metzorah. Rashi asks but the bird has to be burned as part of the עיר הנידחת so how could it be slaughtered for use of the metzorah? Rashi answers it could be burned after it is slaughtered. The Rashash points out that Rashi clearly assumes that the animals must be burned even though the possuk says to kill the animals לפי חרב? He answers that the possuk is referring to animals but birds Rashi would hold is in the same category as the שלל of the city. He cites the Rambam (Avodah Zarah 4:6) disagrees and holds all living creatures get killed. 

The Achronim ask the Gemarah Snhedrin (112a) has a safek if the act of shechitah works at all to remove the tumah of נבילה, so on the צד that it does not how could the Gemarah assume without a possuk one could use the bird for the metzorah if the shechitah will not be valid? According to this Rashash, it is not a question for the Gemarah Sanhedrin is referring to an animal which has a law of killing, then the Gemarah has a doubt if the act of killing as shechitah is just viewed as fulfilling the law of עיר הנידחת, not an act of shechitah at all or it is still defined as an act of shechitah. But regarding birds where there is only a law of burning, the act of shechitah itself will not be defined as fulfilling the law of עיר הנידחת and hence the shechitah will be an act of shechitah. 

The other way the Rashash says is there is no machlokes Rashi and Rambam but that both are done to the livestock, they are both killed and burned. 

In Sanhedrin the Rashash wonders why the Gemarah has a question about the tumah of נבילה if other cases when an animal is put to death such as שור הנסקל the tumah does go off (he cites proofs to this)? It would seem that the Gemarah understands that when there is a law of לפי חרב then the act of shechitah is not defined as an act of shechitah but rather as an act of merely killing the animal and will not remove the tumah but in other places where an animal has a דין to be killed, the shechitah act will still be valid to remove the tumah of נבילה.