I think dogs know words what they have been taught, Which can be loads and loads of words and little sentances.
I speak to my dogs in a way which they do understand, If i come indoors and find my old staffy on the leather sofa, I look at her and say...ahem...And she gets of the sofa lol.
With my deaf dog i have only got to do facial expressions and she knows..or even point to things wile pulling facial expressions and she knows what i mean Clever these dogs of ours