Sensation is entirely a vital function. Consequently it can in no way be said that the angels perceive through the organs of their assumed bodies. Yet such bodies are not fashioned in vain; for they are not fashioned for the purpose of sensation through them, but to this end, that by such bodily organs the spiritual powers of the angels may be made manifest.
Properly speaking, the angels do not talk through their assumed bodies; yet there is a semblance of speech, in so far as they fashion sounds in the air like to human voices.
Properly speaking, the angels cannot be said to eat, because eating involves the taking of food convertible into the substance of the eater.
Although after the Resurrection food was not converted into the substance of Christ's body, but resolved into pre-existing matter; nevertheless Christ had a body of such a true nature that food could be changed into it; hence it was a true eating. But the food taken by angels was neither changed into the assumed body, nor was the body of such a nature that food could be changed into it; consequently, it was not a true eating, but figurative of spiritual eating. This is what the angel said to Tobias: "When I was with you, I seemed indeed to eat and to drink; but I use an invisible meat and drink" (Tobit 12:19).
As Augustine says (De Civ. Dei xv): "Many persons affirm that they have had the experience, or have heard from such as have experienced it, that the Satyrs and Fauns, whom the common folk call incubi, have often presented themselves before women, and have sought and procured intercourse with them. Hence it is folly to deny it. But God's holy angels could not fall in such fashion before the deluge. Hence by the sons of God are to be understood the sons of Seth, who were good; while by the daughters of men the Scripture designates those who sprang from the race of Cain. Nor is it to be wondered at that giants should be born of them; for they were not all giants, albeit there were many more before than after the deluge."
Still if some are occasionally begotten from demons, it is not from the seed of such demons, nor from their assumed bodies, but from the seed of men taken for the purpose; as when the demon assumes first the form of a woman, and afterwards of a man; just as they take the seed of other things for other generating purposes, as Augustine says (De Trin. iii), so that the person born is not the child of a demon, but of a man.