Sentence:  We were forbidden to swing on the gates , lest they <WSD>sag</WSD> on their hinges in a poor-white-trash way , but we could stand on them , when they were latched , rest our chins on the top , and stare and stare , committing to memory , quite unintentionally , all the details that lay before our eyes . 
Meaning of the word marked with <WSD> tags:  droop, sink, or settle from or as if from pressure or loss of tautness