I always thought ETTR was a kind of helpful guideline, "expose for midtones and highlights, get more light on the right side of your histogram," and that was the whole point.  Turns out it's not the whole point.  Exposing to the right is more than a cool idea for generally having more data in your images.  There are some specific actions you can take to optimize exposure in a low-light situation.

I'd say if all you can adjust is shutter in a dark situation, ETTR has more to do with still scenes than moving subjects like your dog or a portrait.  If you want low noise, you're going to want low ISO.  If it needs to be mostly in focus, that limits opening up aperture. What's left?  Your exposure knob and shutter speed.  But really, the principle is to raise exposure all the way to the right without clipping data, however you can.

Take this scene as an example:

This is a dark scene.  ISO 100,  Aperture 5.6, very well-exposed, no noise, but it is a dark scene.  I chuckle as I think of your reaction, "Duh Mr. Smart guy, you just turned your shutter to 25 seconds."  Exactly, but what guide did I use to know how far to turn it without blowing out the highlights?

Compare how this scene would look with our go-to method of raising ISO:

The principal is ETTR, and the guide is histogram.  Specifically, expose all the way to the right, **just to the point before** clipping occurs on the right.  So  if there's a bar on the far right, I've gone too far, back it up 1/3 stop, a click, whatever your measure is.  Now you know that the image will be manageable in Lightroom or whatever your tool of choice is.  In this case, I adjusted exposure in LR down a stop in addition to messing with shadows and highlights.

In Short, ETTR consists of using a tool like histogram to bump right up to but not cross that line of losing data on the high-end.

The two youtube videos that helped me see the light (haha):  The second one is over the top testing on the Sony A7R2.  I hope it helps. 

https://youtu.be/5y2Db2xSVzs
https://youtu.be/gNWWEMS_rEk