This is the 15334th most frequent Polish word.
skwaśnieje
"Skwaśnieje" means "will turn sour."
In this sentence, 'skwaśnieje' is used in a predictive context, indicating a potential change in condition of the milk due to environmental factors.
Mleko skwaśnieje, jeśli zostanie na stole przez całą noc.
The milk will turn sour if left on the table overnight.
Here, 'skwaśnieje' metaphorically describes the change in mood or temperament as a response to upsetting news.
Jej humor skwaśnieje, gdy dowie się o tych kłopotach.
Her mood will turn sour when she learns about these troubles.
'Skwaśnieje' in this sentence refers again to the literal spoilage of a consumable liquid when exposed to unsuitable conditions.