The inside of the armored vehicle was cramped, oppressive, and dark. It became even more crowded and stifling after squeezing in seven fully-armed men. At this time, the firing ports had to be open.
Armored vehicles are designed for combat, not comfort. Safety is the priority.
But looking out through the narrow firing port, one saw a yellow face and a pair of indifferent eyes. It was a shock that the armored infantry could never have imagined.
Then consider another scenario, you're sitting on a plane, looking out the window, and suddenly, right outside the window next to you, is a face coldly staring at you.
"Ah!"
A sharp scream immediately rang out.
Gao Yuan had frightened someone badly, and he, too, was startled. Gao Yuan's response was to immediately throw his head back and then, instinctively, he stuffed a grenade into the firing port, dropping it into the crew compartment.
How terrifying, enough to scare someone to death.