About five years ago, my family was caring for my brother's dog - a German Shepard-husky-chow-chow mix, an incredibly gentle dog who never barked.
One day me and my sister came home from school and like every other day he greeted us through the upstairs rails and came about half way down the stairs where he laid down and watched us.
Just as we put our backpacks down we heard it. The little spot upstairs right before the steps, that let you know you weren't alone, creaked...and right after the creak the shuffling followed, like something running away after getting caught.
Me and my sister just stood there, I wanted to scream and run out the house, but we stood there frozen not knowing what to do.
Then the dog immediately stood up and bared his teeth. He was facing towards the stairs and all the hair on his back started to rise.
He chased whatever it was, barking and growling the whole time. It sounded like he was going to freakin' kill something! Then out of nowhere he stopped and came downstairs and stayed by our sides until our dad came home an hour later.
Of course our dad didn't believe us, stuff like that never happened to him so it didn't exist. That is one of the creepiest things that ever happened to us, and it never happened again after that day.