Imaginably I had all stupid dogs, but I seriously question whether they can truly understand words other than perhaps their names. I think it’s actually all in the way a person says the words.
The smartest dog I ever had was an excellent cattle dog. I had a number of commands for her, directing her to do some fairly complex things. But it was really the intonation, the word rhythm and accompanying gestures, also whistles. If, say, I varied the tone, the rhythm of the words or the gestures, she “didn’t get it” at all or would do the wrong thing. If I made one verbal commend sound like another, with the intonation like the second instead of the first, she would follow the second, not the first.
I even question whether they really know their names in the way we do. There are a limited number of ways we address a dog, and they learn all of them mean they must pay attention. So then they watch for other clues. I do think tone, number of syllables, eye contact, facial expressions and movements are what they learn, not words.
And it’s natural that they would. That’s the way it is with wolves. They don’t say words to each other, but they have a lot of ways to communicate a lot of things, including tone, posture, movements, eye contact, facial expressions.
Sorry, but I don’t buy the idea that they really understand words in the way we do.