Sometimes Nebbie will suddenly stare at the wall next to the door.
I sort of wonder if they can hear subtle movements in the building's structure shifting. Yanno, when the wind blows and the buildings shift enough for us humans to hear...I'm sure there are tiny ones we don't hear.
Nebbie will look at the ceiling, when my dad is very active upstairs - but at least I know what she's trying to see!
Paizly's too lazy to care. The only time anything disturbs her, is if the doorbell rings. If she's in bed with me, she'll scramble under the covers... or if she's on her own in the room, scramble for some "safe" place like her paper grocery bag or a nook by the fish tank. Oh, and she growls...sounds like she wants a fight, while at the same time running for her life. Hilarious!