What is the scariest ""canary in the coal mine"" moment you've ever experienced?

Friends and I were hiking out in Colorado on a 2 day backpacking trip. We hiked about 9 miles the first day and set up camp close to treeline as we were planning on doing some climbing the next day. On that hike, about 5 miles in we started seeing large claw marks down trees here and there, we brushed it off until we saw what looked to be pretty fresh mountain lion tracks. While hiking the rest of the way to camp I couldn't shake the feeling that I was being watched. That night my friend swears he saw a large blurry shape rush through the trees about 50 feet away. Nothing else happened but I definitely didn't sleep much that night and it felt great to pack up and hike out of there.