is there a mitzvah to kill the animals of Amalek

My son’s Rebbe once asked the following question: Rashi on chumash (Devarim 25:19) explains that the mitzvah of destroying Amalek applies to every man, woman, and child, and even the animals which belonged to Amalek, so that Amalek should not be remembered by people saying “This is the ox of Amalek.” Yet, in Sefer Shmuel in the haftarah which describes the command to Shaul to eradicate Amalek, Rashi explains that the animals had to be destroyed because Amalek were experts at witchcraft and could make themselves appear to look like animals. The implication of this Rashi is that killing the animals to eradicate the memory of Amalek is not inherently part of the mitzvah, except for the fact that an animal may be a person in disguise. Aren’t these two statements of Rashi contradictory?

As we know, Shaul spared the life of Agag and the animals, failing to fulfill G-d’s command. Whatever the fault and sin involved in this act, it is hard to understand the audacious response of Shaul when confronted by Shmuel. He tells the Navi, “Kiyamti es dvar Hashem” – I fulfilled G-d’s command! Could Shaul have been so brazen or so self-deluded to think this statement would go unchallenged?

The Oneg Yom Tov offers a brilliant explanation of Shaul’s logic. Surely if someone purchased an animal from Amalek a month, a week, or even a day before the war started, that animal would not have to be killed. That animal would not longer be the property of Amalek – it would be the property of its new owner, completely divorced from Amalek. Using this legal loophole, Shaul realized there was a way to spare the life of all the sheep and oxen of Amalek. So long as someone from Amalek could relinquish ownership of their animals, those animals would not have to be killed. Therefore, Shaul deliberately left Agag, not to spare his life, but simply to pressure him to first declare hefker the animals of Amalek so they could be acquired by new owners before the battle was over. Shaul figured he could use this loophole both fulfill the technical obligation of waging war and at the same time salvage the animals for better use.

Why did the Navi object? Not because of any fault in the logic of the legal loophole, but because of the use of the loophole itself. G-d does not want us to try to “outsmart” his mitzvos with cheshbonos that depend on the use of every technicality in our legal arsenal to circumvent the plain meaning of his directive. We are responsible for fidelity to the spirit of the law as well as its technical details.

Aside from being a powerful mussar, I think the Oneg Y”T can help answer the contradiction in Rashi. Rashi in chumash teaches that an animal found in Amalek’s possession must be destroyed to obliterate their memory. Rashi in Sefer Shmuel is explaining why even an animal which Amalek declares hefker on the cusp of battle should still be killed lest that declaration of hefker to spare the animal actually serve to spare the life of a disguised Amaleiki.