19. Some also are killed by means of a little bird called the trochilus, which, while seeking for some picking of small food, and flying gently about the beast while asleep, tickles its cheeks till it comes to the neighbourhood of its throat. And when the hydrus, which is a kind of ichneumon, perceives this, it penetrates into its mouth, which the bird has caused to open, and descends into its stomach, where it devours its entrails, and then comes forth again. 20. But the crocodile, though a bold beast towards those who flee, is very timid when it finds a brave enemy. It has a most acute sight, and for the four months of winter is said to do without food. 21. The hippopotamus, also, is produced in this country; the most sagacious of all animals destitute of reason. He is like a horse, with cloven hoofs, and a short tail. Of his sagacity it will be sufficient to produce two instances. 22. The animal makes his lair among dense beds of reeds of great height, and while keeping quiet watches vigilantly for every opportunity of sallying out to feed on the crops. And when he has gorged himself, and is ready to return, he walks backwards, and makes many tracks, to prevent any enemies from following the straight road and so finding and easily killing him. 23. Again, when he feels lazy from having his stomach swollen by excessive eating, it rolls its thighs and legs on freshly-cut reeds, in order that the blood which is discharged through the wounds thus made may relieve his fat. And then he smears his wounded flesh with clay till the wounds get scarred over. 24. This monster was very rare till it was first exhibited to the Roman people in the ædileship of Scaurus, the father of that Scaurus whom Cicero defended, when he charged the Sardinians to cherish the same opinion as the rest of the world of the authority of that noble family. Since that time, at different periods, many specimens have been brought to Rome, and now they are not to be found in Egypt, having been driven, according to the conjecture of the inhabitants, up to the Blemmyæ[135] by being incessantly pursued by the people. 25. Among the birds of Egypt, the variety of which is countless, is the ibis, a sacred and amiable bird, also valuable, because by heaping up the eggs of serpents in its nest for food it causes these fatal pests to diminish. 26. They also sometimes encounter flocks of winged snakes, which come laden with poison from the marshes of Arabia. These, before they can quit their own region, they overcome in the air, and then devour them. This bird, we are told, produces its young through its mouth. 27. Egypt also produces innumerable quantities of serpents, destructive beyond all other creatures. Basilisks, amphisbænas,[136] scytalæ, acontiæ, dipsades, vipers, and many others. The asp is the largest and most beautiful of all; but that never, of its own accord, quits the Nile.