I think they understand voice tone and facial expressions as well.
Yes, I think they understand that in terms of whether you are pleased with them or not.
Oh yes, facial expression is very well understood by dogs.
I have a deaf Great Dane and he knows exactly what is what, from my facial expression alone.
It definitely takes time and you have to be committed to train them.
OTOH, facial expressions goes both ways. I can tell when they’re up to no good. 😊
Oh no doubt they understand tone and expressions. They are absolute masters at reading body language. Somehow my 7 year old Lab knows the exact nanosecond I’ve decided to take him outside. He knows it before I even move a muscle. The same is true for getting his dinner or otherwise getting him something he wants. Obviously I must be giving off some kind of sign even if I don’t know exactly what it is. He sure knows.