My dog is deaf, and I whisper when I want to communicate with him. I find lowering the timbre of my voice accentuates the movement of my mouth. My dog is smart; he can lip read.
My cat, on the other hand, is blind. He is a work in progress.
In real life, Steven’s dog feigns deafness, and his cat is merely short-sighted, but both are willing to play along in aid of dramatic effect.