Girls of a certain complexion, at certain times in particular climates, blush with their knees. It’s not a scraped or bloodied redness, just the same flush that rises to the cheeks of most such girls in exertion or embarrassment.
The girl’s response is typically negative. That which is not smooth and even must be cured or concealed: pants, thigh-highs, even foundation.
That response is misguided. The blushing knee is the orbital laser strike of seduction, and it hits Fenimore foursquare, as Alma steps up out of the little boat. He’s atoms. Alma, perfectly innocent, just ran out of untorn hose.