They do make an effort to learn, which is remarkable considering their natural way of communicating is very different from ours.
When my family lived in Indiana, we were several miles out of town, and had a septic tank. Naturally, they need to be cleaned every five years or so. The man who came to do that had a dog. I think it was a black lab; in any case it was large and black. He'd trained it to be more or less his assistant. If he needed a tool, he'd ask the dog to get it, and the dog always chose the right one. When he was done, and needed to give my mother a receipt, he told the dog to go get his book and pen. The dog went to the truck, opened the door, climbed in, found the book and pen, and delivered them.
It was quite impressive. He wasn't really giving "commands". He just spoke to the dog conversationally.
