someone's jaw drops (open)
US /ˈsʌm.wʌnz dʒɔː drɑps (ˈoʊ.pən)/
UK /ˈsʌm.wʌnz dʒɔː drɑps (ˈoʊ.pən)/
1.
used to say that someone looks very surprised or shocked
:
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When she announced her engagement, everyone's jaw dropped.
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My jaw dropped open when I saw the price of the new car.