I came home tonight and he was on the printer again, deeply in dead cat sleep, and I stood in front of him yelling his favorite words - his name, and Dinner! Nothing. Not an ear twitch of acknowldgement.
Then, a couple of hours later, Girl called and I told her my theory, and Boris was standing in front of me, looking away, so it was a fine time to test it. I yelled his name a few times. Nothing. Boris used to have very sharp hearing - the joke was that you could say, or whisper, his name anywhere, anytime, and he would hear it and start purring loudly.
He's 13, and has had no ear issues, so this is out of the blue. But I may as well stop swearing at him, because all it is doing is straining my voice. Time to stop hollering at the deaf cat.