This is the 1406th most frequent Polish word.
twarzy
"Of the face" (genitive singular form of "twarz").
Here, 'twarz' is in its singular form, 'twarz', indicating the concept of 'face' as part of the body.
Dziewczyna zasłoniła twarz rękoma.
The girl covered her face with her hands.
The word 'twarzy' here is in the genitive ('on the face'), commonly used when describing something appearing on the face.
Na twarzy chłopca pojawił się uśmiech.
A smile appeared on the boy's face.
In this sentence, 'twarzy' is in the genitive case, referring to the expression visible on the facial features.