This is the 14305th most frequent Polish word.
przebiera
"Przebiera" means "dresses" or "changes clothes."
Here, 'przebiera' refers to the act of Kasia changing her clothes into a costume.
Kasia przebiera się za księżniczkę na bal przebierańców.
Kasia is dressing up as a princess for the costume party.
In this context, 'przebiera' illustrates the repetitive motion of the child's legs.
Dziecko przebiera nóżkami z niecierpliwości.
The child is moving its legs impatiently.
Here, 'przebiera' means to sort or sift through something while making a selection.