、。
I stared at the man, too stunned to speak.
Literal
Dumbfounded thing [even-も] unable-to-say [without-ずに], that man [object-を] stared-at
呆気に取られる (あっけにとられる) = to be dumbfounded/struck speechless. 物も言えずに = 'without being able to say even a thing' — 物 (thing) + も (even) + 言えず (unable to say, using the literary negative ず) + に (adverbial). ~ずに is a literary equivalent of ~ないで. 見つめる adds intensity beyond 見る.