It occurred to me recently that when you describe a dog “shaking,” it could mean one of three things. Which of these do you immediately think of if someone says a dog is shaking?
When dogs shake off water, it’s over so quickly that you don’t have time to say “the dog is shaking” before it’s over.
And just as you wouldn’t say “those two people are shaking” if they are shaking hands, I wouldn’t interpret your statement to mean that a dog is offering his paw for a handshake.
The first, and only, interpretation I can link you statement to is the image of a dog shivering due to cold or fear.
Nah! I’ve got Wiener Dogs, and they all do it the same. They start with the head/shoulders, then a wave kinda rolls down their bodies till it gets to the rear end. Then the hips starts shaking and it finally goes down to the end of their tails.
Takes about 10 seconds. Usually telegraphed by a long stretch.
My first thought was “the poor thing has epilepsy.”
Up until we got our current dog, I would’ve voted for the thing they do when wet. However, our current dog is part chihuahua, so barely an hour goes by when he doesn’t shiver. So now, if I hear that the dog is shaking, that’s what I think of.
If a dog is shivering from cold or fear, that’s something worrying and worth remarking on. Shaking off water is more normal, and less likely to be commented on. I also agree that it’s over so quickly that you’re unlikely remark on it while it’s actually happening.
My first thought was wet dog air-drying himself, because that’s something they do often (even when not actually wet). And the phrase would be used plenty in that context, usually followed by the words “all over <something>”.
My second thought was a dog offering his paw to shake extremities with a person, that being a common trick.
My third thought was a dog with some sort of palsy or other condition. I’ve never met a dog with such a condition, but they’re enough like us that I’d expect it’d be possible.
It never even occurred to me that a dog might shiver in fright, because all the dogs I’ve known have shown fear in other ways (most often by whimpering and by trying to hide).
Context decides this. If there is none, then I think they are shaking with fear, as happens at the vet, for example.
My Yorkie shakes on command after I bathe her. She waits til I tell her to shake and then does it. She is incredibly dumb, it’s really her only trick except ‘sneeze’. Luv her though!
I was sure this thread was going to be about Chihuahuas.
I thought about a dog shaking from cold or fear first, or shivering. Then I thought about a dog raising his front paw so you can shake it.
I would. Why wouldn’t you? I even give my dog the command “shake” when I want him to shake hands.
I didn’t think of a dog shaking water off himself, at first, but when my dog gets wet and I can see he’s about to shake himself dry, I’ll say “shake.” Then after he shakes himself off, I’ll say, "Good boy, " just for shits ‘n’ grins. 
There is a dog I know that every time there is thunder (and many times when it is only raining) he vibrates like a marital aid.
Our dog shaking water off after a dip in the pool. Right in front of the sliding glass doors. Which I just finished cleaning.
Mine, too, especially because a dog that we used to have suffered from it.
I voted the second option because my dog used to shake when it thundered. It made me so sad!
Thankfully she has gotten more brave with age.
First thing that came to mind was the “classic” slo-mo shaking dog
I voted for #2. I know people that own chihuahuas.
I’d call that “quaking” or “trembling”. Because it’s summer and our dogs are in the water a good bit, I thought of them shaking off water. I call the paw thing “giving paw”, and the command I use is “Paw”.
ETA: nm
cold, fear - or excitement - I have a Boston who is like a stuck wind-up tin toy when he’s excited.
My Grady is a non-Chiuhahua, 50-lb mutt. He shakes with excitement all the time, even when there doesn’t seem to be anything THAT exciting going on. His back end shakes.
He actually doesn’t shake in the same way when he’s afraid of thunder. That’s a different, whole-body shake.
Anyway, I voted “other” just because I’ve got a trembly dog.