Clara's Unease in the Evening Silence

Read the following excerpt from a novel:

As dusk fell over the quiet town, a sense of unease settled like a heavy blanket. The streets, usually bustling with the laughter of children and the chatter of neighbors, were now eerily silent. Clara stood by her window, her heart racing. What was it that had shifted in the air? She took a deep breath and peered out, noticing the shadows elongating across the pavement. Something was not right, yet she couldn't pinpoint what it was. When had this place, which she had always considered a safe haven, transformed into a realm of uncertainty?

According to the excerpt, what most significantly contributes to Clara's feeling of unease?