I have a new answer to that question as of today, thanks to a guy who was playing at Harrah's Cherokee this afternoon with Nina and me.
A pet bird.
Not in a cage.
Inside his shirt.
My awareness of this oddity began when I heard a brief, high-pitched "tweep," which Nina later correctly compared to the chirp a smoke detector makes when its battery is running low. I figured it was some sort of notification on somebody's smart phone, and didn't think much more of it.
But a few minutes later I heard it again, and was better able to localize the direction it was coming from. I looked at the guy, and there is a BIRD POPPING ITS HEAD OUT OF HIS SHIRT COLLAR.
Mind you, this was not a stuffed bird. It was not a toy bird. It was a real, living, honest-to-goodness pet bird--a peach-faced lovebird, to be exact.
It would pop in and out of his shirt. It was out for quite a long time, sitting on his lap, as he fed it some birdseed from a little tray that he had brought along. When it chirped for attention, he would stroke and kiss it gently and talk to it softly. The bird's name is Smokey. It bit him once, and got a mild scolding, but otherwise was very well behaved. It never tried to fly away.
I know what you're thinking: "Pics or it didn't happen."
Well, OK then:
He gave me permission to take this picture, but for some reason wanted to partially hide his face.
Here's a super-cropped close-up of the bird from another shot I took a few seconds later:
I wonder how many bird poops there are inside his shirt.