I was elk hunting alone in Montana years ago and sitting with my back to a thicket of brush looking over a big valley. Just as it was getting dark and it was time to pack it in a damn cougar let lose with a howl in the brush behind me.
Rifle had a scope on it so it was worthless, walked the whole way out with my handgun out, almost got frostbite on that hand. :)
The incident in Montana was in front of my house, in the dark taking my puppy out before bed. The lion had patterned our evening outings and was in a tree not far from my puppy’s nighttime spot. I heard it jump down from the tree and put my flashlight on it. Every damn hair on my body was standing at attention as I called the puppy to me and backed the 50 yards to the house.
I never walk my property without a firearm now ... and the dog is always on a leash at night.
The most terrifying sound they make comes from females in heat.
It's a sort of scream that sounds like a teenage human girl screaming defensively. When you hear it in the middle of the night from a dark, wooded canyon, it really does make the hair on your neck stand up!