Complex sentence: Seconds later, she appears next to the window with a gas mask, holding a nozzle with which she sprays the occupants of the car with what is apparently a knockout gas, causing them to become unconscious.
Split into simpler sentences: Seconds later, she appears next to the window, wearing a gas mask. She is holding a nozzle with which she sprays the occupants of the car with what is apparently a knockout gas, causing them to become unconscious.