Scholion to Iliad 1.50:
[1.50: “First he set upon the mules and the swift dogs.“]
The god, being a lover of humans, first did away with the mules and the dogs and the other unreasoning beasts, so that, leading the Greeks to fear through their example, he could turn their minds to piety. Or it may be that asses and dogs have a more powerful sense of smell. For dogs often perceive animals from the smell of their tracks, while quite often mules who have been left behind by people have found their routes from their sense of smell.