agape1
adjective /əˈɡeɪp/
  /əˈɡeɪp/
[not before noun] (formal)- if a person’s mouth is agape, it is wide open, especially because they are surprised or shocked(嘴巴因吃惊等)大张着 - He watched the spectacle, mouth agape.他目瞪口呆地看着这一奇观。 
 
- He watched the spectacle, mouth agape.