いた くちがふさがらない
aitakuchiga fusagaranai

i-Adjective
Idiomatic Expression

1. dumbfounded; speechless; flabbergasted; openmouthed (with surprise)

その返事 へんじには ひらいた くち ふさがらなかった。
sono henjiniwa hiraita kuchiga fusagaranakatta.
I was taken aback at the answer.
Other forms: