A significant percentage of time, I find that pedestrians think "on your left" means move left, or they are among the scary proportion of people that can't discern left from right on a moment's notice. And many pedestrians have headphones and won't hear my proclamation. So I call out on a case by case basis. But I am more likely to call out to someone with an animal because a collision is likely going to hurt me more than the animal.

All that said, animal walkers need to keep their animals usually on their right. Always stay between the animal and the pedestrian and bicycle traffic that is oncoming or overtaking. Better yet, keep the animals at home. And if you rip me off my bike and/or use my bike to pin me down for any reason, you're likely going to die.