The Signal

Sarah and David were driving through a dense forest when their car broke down miles from civilization. With no cell service, David decided to hike back to the nearest gas station. Before leaving, he gave Sarah strict instructions: 'Lock the doors. Do not open them for anyone unless you hear three distinct knocks. That's our signal.' Hours passed in the suffocating darkness. Eventually, Sarah began to hear dull, heavy thuds against the roof and door of the car. Sometimes slow, sometimes rapid, but never the rhythmic three. She sat paralyzed in the driver's seat until dawn, never unlocking the door. What was happening outside?