Pengrych's desperate flight carried him through these dense lakeside woods.

Time passed.  Curiously, the babies’ development seemed retarded, and, if anything, they grew uglier all the time.  This aroused the parents’ suspicions, and the father eventually declared that the boys were not his sons.  In despair, the woman went to see a gwr cyfarwydd (wise man or conjurer), who offered traditional advice on how to recognize changelings.  The woman returned home, and the next day, while her husband and a farmhand were at work in the fields, she set her trap.

In full view of the twins, she began to prepare the meal for the day—in an eggshell!  The boys, curious, asked what she was doing.  When she replied that she was preparing the main meal of the day, the children, in astonishment, revealed themselves as changelings by blurting out:

Acorns before oak I knew,
An egg before a hen,
Never one hen’s egg stew
Enough for harvest man.

Upon hearing this, the wife seized the changelings, dragged them outside, and threw them into the pool.  The fairies immediately appeared, rescued their young, and restored the woman’s own.

The loss of fairy sight

This story and others of its type all follow the same pattern.  The eggshell test and giveaway fairy recital are consistent elements.  One curious characteristic of the tales is that fairies only steal male babies.  The general explanation for this behavior was that the fairy people were so sickly and ugly that they hoped that interbreeding would strengthen their race.  The deficiencies in fairy males are also illustrated by the fact that there are no stories of fairy men marrying human girls.  On the other hand, there are a great many accounts of young men capturing and subsequently marrying fairy maidens.  These marriages were usually on the condition that the husbands never struck their wives, either needlessly or with iron.  In such circumstances, the fairy woman invariably disappeared.