Dark rectangle moved slowly across sky with swaying motion, possible telepathy with 2nd observer

Walking down an alleyway between two-story warehouses with a friend, had an urge to stop and  look directly above me. As I looked up an object slowly floated into view. It was rectangular, dark and moving VERY slowly. 
I thought at first it must be a plane but could see no blinking lights or light of any kind, then of course nothing where a fuselage would be, and what would be wings weren't swept back and were squared off and not tapered like wings. There was no sound. It was only visible because of the city light vaguely illuminating it's underside. 
My friend had continued on several yards still talking to me, noticed that I had stopped and was looking up at something. So he looked up to see what i was looking at. By the time he saw the thing it had moved about a third of the way across the piece of sky that we could see.  I was starting to notice all kinds of unusual detail on the thing, like rods protruding and lines underneath.
And there was really something strange about the way it was moving. And another REALLY odd thing was... I seemed to be able to hear the thoughts in my friends head.
It seemed that once he noticed the strange motion, that it seemed to move a liitle and then stop, move and stop, like it was swaying, but not side to side but up and down, I thought I heard him think to himself "Is it a Bird?" Then I said out loud to his unvoiced question "No, it's not a bird" 
We stood there transfixed, watching as it moved out of view behind a building. I ran to the end of the alley to try and spot it again but there was a bright street light in my eyes. My friend stood there transfixed, he said more because of me reading his mind than what we had seen.
Witness indicates that date of sighting is approximate.  PD