Sentence:  We were forbidden to swing on the gates , lest they sag on their hinges in a poor-white-trash way , but we could stand on them , when they were latched , rest our <WSD>chins</WSD> 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:  the protruding part of the lower jaw