In the Haftorah for parshas Zochor we read that Hashem commanded King Shaul not only to destroy all the Amalekites, but also all their animals. Why was there a need to destroy also the animals?
Rashi to Shmuel Aleph 15:3 explains that the Amalekites were sorcerers and were capable of disguising themselves as animals - and for this reason Shaul was commanded to kill even the animals.
In his commentary to Devarim 25:19 he brings another explanation: The eradication of the memory of Amaleik had to be absolute, and even if animals remained alive they would serve as a reminder of the nation. Every last animal had to be wiped out in order to ensure, "That the name of Amalek should never again be mentioned, even regarding an animal, to say: 'This animal was from Amalek.'"