I let him go, and watched him wander over to one of the windows and jump up onto the windowsill and maneuver his head between the curtain and the glass, so that his rump and tail were visible to me but his head was hidden except for the shadow it made against the fabric. His tail twitched now and then in reaction to something he could see outside. I imagined it was a bird or a squirrel that he was reacting to, as that is what he and the other cat most often seem to be looking at when they position themselves on the windowsills.