After I was in bed, surrounded by various animals, reading in the bedroom, I heard a sound similar to the door buzzer. I wasn't sure but thought it wasn't actually the door buzzer, and if it were, I wasn't about to get up and ask who was there. It was about eleven at night and I sure don't know anyone in NYC. I heard the sound again after a few minutes. It made me nervous but I'm not sure why.
Then Floyd started growling. He sat at the end of the bed, facing the dark hallway and living room, and growled. I looked into the darkness to see if I could discern any movement. I had no plans for any kind of escape and I sure didn't want to engage anyone who might have gotten in. But of course I could not sleep if someone had gotten in. Floyd continued to growl. After something of an eternity I finally stood up and turned on the nearest hall lights and made my way into the living room. One good thing about a small apartment is just that: it's small. I could see immediately that nobody was inside and I checked the door to confirm that I had locked it (I had). I could hear voices from the street but none from inside the building so I do not know what set Floyd off.
I turned off the lights and went back to bed and Floyd stopped growling. I guess I'll never know.