Dogs spooky reaction

     Last night, our youngest dog, who sleeps at the foot of our bed; she's a good foot warmer, really spooked us. What she heard or thought she heard, I have no idea. My wife and I had turned in about midnight. I was awakened by the low gutteral growls of this youngster. My wife was already awake and motioned me to keep silent. The growls continued for a while and as the dog is coal black I had a hard time seeing her even though she was only a few feet from my nose. The elder dog is grey and sleeps next to the heat register. His bed is light colored and I could see that he was not awake, but curled up in a ball. Our black dog stood up and leaned out away from the bed as far as she could without falling out of the bed. She was trying to see down the dark upstairs hall. I looked at our clock which read 4:15. The growling continued, low, like a warning growl. Finally, my curiosity got the best of me and I got up and walked down that hall to the bathroom which is on the opposite end. I saw nothing, I heard nothing. Just to be sure, I walked downstairs and checked the rear door which was solidly locked. I still heard nothing but the ticking of a clock. So I went back upstairs and back to bed. Our little black schnauzer was still sitting up at the foot of the bed. When I got back in bed, she settled back down and I suppose she then went to sleep. Did she sense something? Did she hear a mouse? I have no idea, but until you experience something like that, you have no idea how creepy it can be.