The way of an eagle - I borrow, with thanks, the very sensible note of the Rev. Mr. Holden on this passage.
"The particle כן ken plainly shows that Proverbs 30:19; and Proverbs 30:20; are to be taken in connection; consequently, it is a comparison between the way of an adulterous woman, and the way of the things here described.
"The adulterous woman goes about in search of her deluded victim, like as the eagle takes its flight into the air to spy out its prey. She uses every species of blandishment and insinuation to allure and beguile, as the serpent employs its windings and sinuous motions to pass along the rocks; she pursues a course surrounded with danger, as a ship in the midst of the sea is continually exposed to the fury of the tempest, and the hazard of shipwreck; and she tries every means, and exercises all her sagacity, to prevent the discovery of her illicit enjoyments, as a man attempts to conceal his clandestine intercourse with a maid. Such is the conduct of a lewd woman, marked by specious dissimulation and traitorous blandishment; she eateth and wipeth her mouth-she indulges her adulterous lust, yet artfully endeavors to conceal it, and with unblushing countenance asserts her innocence, exclaiming, I have done no wickedness."
Chaucer's January and May is an excellent comment on such wiles and protestations.
The way of a man with a maid - בעלמה bealmah with or in a maid; but one of De Rossi's MSS. has בעלמיו bealmaiv, in his youth; and with this the Septuagint, ev neothti, the Vulgate, in adolescentia, the Syriac and the Arabic agree; and so also my own MS. Bible: - The weie of a man in his waxing youthe. Dr. Kennicott, in a sermon preached at Onsford, 1765, p. 46, has defended the reading of the versions, corroborating it by two MSS., one in the Harleian, and the other in the Bodleian library, besides that mentioned by De Rossi. See De Rossi's Var. Lect. Certainly the way of a man in his youth contains too many intricacies for human wisdom to explore. He only who searches the heart knows fully its various corrupt principles, and their productions. The common reading may refer to the formation of a child in the womb. But some have understood it of the immaculate conception. See my note on Matthew 1:23; (note), where the subject is largely considered.
If we take the four things which Agur says were too wonderful for him, in their obvious sense, there is little difficulty in them.
And as to the fourth, if it refer to the suspected incontinence of one reputed a virgin, the signs are so equivocal, as to be absolutely unascertainable. The existence of the hymen has been denied by the ablest anatomists; and the signs of continence or incontinence, except in the most recent cases, are such as neither man nor woman can swear to, even to the present day; and they were certainly not less difficult to Agur and his contemporaries. I shall carry this matter no farther.
Another enigma. The four things of Proverbs 30:16 agreed in the common point of insatiableness; the four now mentioned agree in this, that they leave no trace behind them.
Proverbs 30:19
The way of a man with a maid - The act of sin leaves no outward mark upon the sinners.