What did Elisa use for knitting shirts to rescue her brothers from a spell in "The Wild Swans" fairy tale?

"The Wild Swans" is a literary fairy tale by Hans Christian Andersen about a princess who rescues her 11 brothers from a spell cast by an evil queen.

In the story, there lives a widowed king with his twelve children: eleven princes and one princess named Elisa. One day, he decides to remarry, but marries a wicked queen who is a witch. Out of spite, the queen turns her eleven stepsons into magnificent swans, who are allowed to temporarily become human only at nights, and forces them to fly away.

Elisa is guided by the queen of the fairies to gather stinging nettles in graveyards to knit into shirts that will eventually help her brothers regain their human shapes. Elisa endures painfully blistered hands from nettle stings, and she must also take a vow of silence for the duration of her task, for speaking one word will kill her and her brothers.

Hans Christian Andersen (2 April 1805 – 4 August 1875) was a Danish author. Although a prolific writer of plays, travelogues, novels, and poems, he is best remembered for his fairy tales.

Hans Christian Andersen was born in Odense, Denmark on 2 April 1805. He had a half sister named Karen. Andersen's father, who had received an elementary school education, introduced his son to literature, reading to him the "Arabian Nights".