What is the meaning of "吃这一声"? For context the entire sentence is, "吃这一声，周昂忽然一下子睁开了眼睛。" Is it supposed to be something allong the lines of, "[the sound of] eating, this single sound"? This sentence isn't making much sense to me.
The verb 吃(eat) has the extended meaning of 受(take) and the object has to be a physical contact or impact 

Example:

吃一發子彈 (eat a bullet) = (take a bullet/ take a gun shot)

吃一拳 (eat a punch) = 受一拳 (take a punch)

吃一記耳光 (eat a slap on the face) =  (take a slap on the face) 

吃这一声 is not grammatical. because a sound doesn't make physical contact with the subject. The phrase should be written as  聽了这一声 (heard this sound)