Foreshadowing in Narrative

In literary works, foreshadowing plays a crucial role in enhancing narrative depth and building suspense. Consider the following excerpt from a fictional novel where the protagonist, Sam, has just returned to his hometown after many years:

"As Sam stood at the edge of the old park, he felt the sharp chill in the air beneath the darkening sky. The swing set, now rusty and covered in vines, creaked eerily in the wind. Nearby, a dog howled mournfully, its sound piercing through the heavy silence. Sam's childhood memories flooded back, but they were shadowed by an unsettling premonition of change looming ahead. A flicker of lightning illuminated the dis\tant hills, and in that moment, he couldn’t shake the feeling that something, or someone, was watching him."

Which of the following details from the excerpt serves as the most significant ins\tance of foreshadowing?