Sentence:  But after the doctor 's return that night Alex could see , from the high window in his own room , the now familiar figure crouched on a truly impressive heap of towels , apparently giving its egg hatching powers <WSD>one</WSD> final chance before it was replaced in its office by a sure-enough hen . 
Meaning of the word marked with <WSD> tags:  having the indivisible character of a unit