Englishopen-mouthed
adjective
they stare at us open-mouthed, as if we are completely insane:
astounded, amazed, in amazement, surprised, stunned, bowled over, staggered, thunderstruck, aghast, stupefied, dazed, taken aback, shocked, shell-shocked, in shock, nonplussed, speechless, dumbfounded, dumbstruck, tongue-tied, at a loss for words, agape, goggle-eyed, wide-eyed, staring;
informal flabbergasted;
British, informal gobsmacked.