When I see dogs in other people's cars I bark at them. I want to say hello. The experts don't encourage this:
"One thing you have to bear in mind is that there is no such thing as an official dog language. When dogs communicate with one another it is through body language and tone. So, when you hear dogs barking at one another the key thing that they are listening to is the type and tone of the bark."
And yet there so many videos on how to bark like a dog and have conversations with your pet. Are we learning to distinguish the types and the tones of barking? I haven't investigated this.
I go with this approach: "if he starts wagging his tail, jumping up excitedly, and is clearly happy, the chances are he likes what you are ‘barking’ to him." And usually dogs getting a bark greeting in cars get excited so seem to like it.
Sometimes Millie sits there with her head to one side - which is dog language for what is this supposed to mean? - I do the same. The would likely lead to double confusion. But it seems fun at the time.
And Baxter? The experts say that cats do not meow at each other. They meow at humans. Here's the meow interpretation:
The m- or mrr-sound is a pleasant sound that the cat uses for people it likes. If the e of the meow is stressed, it can signal physical discomfort, such as that the cat is hungry or cold. The meow that cats use most with humans has a long ah-sound. If the person doesn’t respond, the cat becomes frustrated and the ow-sound becomes more pronounced, almost like a howl.
I remember that Baxter learned the last one when he was boarding at the vets one time. He came back with a loud and prolonged set of meows that he now prefers. Another grunge abstract with numbers. | 
