Hah! I have two cats, my male cat loves to hear the acoustic guitar, and will often stick his head against it (longer than a rub). The bass, he’s not too sure of.. He will try to bite the strings, I think because he can really see them vibrate.
Myother cat could care less about music.
My dog was only interested in seeing and sniffing the bass when she saw it for the first time. After that, she hasn’t been interested in it at all. She walks past me while I’m playing, when she’s going to the balcony, and stands in front of the door so I have to get up and open the door for her. I also have to stop playing and go open the door again when she wants to come back in. 
I guess for her the bass is just one of the weird things only humans are interested in.
There is a long-standing thread for pet pictures.
I know that, but I chose to resurrect this thread because its title more closely matched what I was posting.
My moms dog hates it, I think it’s because I play before walking him, so bass=waiting time (?)
One of my cats loves it, she sits on my shoulder when I play or in my lap and rubs the bass when she likes the song, sometimes she places her paw on the String and is happy when she creates a sound (yes I have tricked her into believing she played a couple notes)
my other cat is indifferent to it, but sometimes peeks in and sits next to me
My Great Pyrenees howls at the open E string. And only that! Is he criticizing or accompanying?
Try a Siberian husky, they usually howl at every note 
My friend’s husky howls when she plays guitar. It is cute, because he clearly wants to be in the band.
I think for your dog, the open E resembles howling, so he joins in. 
On the topic of dogs and singing. I have a friend who is a singing teacher, and one of her dogs learned to howl at the same key she is singing. I thought it was interesting and once found in the Internet information about that (teaching a dog to sing at a desired note), but unfortunately I can’t find it now.
But I was able to find a YouTube channel, which has videos about this same subject. Here’s one of the videos, where the owner is playing a note on the piano while singing the note to her dog, and coaching the dog to sing at that key. The dog is praised when she successfully sings at the right note:
Oh my goodness, now she can sing scales too! It’s amazing what a dog can learn. Actually the teaching method is not that different than for teaching humans. Except all the praise and promises of treats
