It appears that dogs can detect injustice and be upset about it:
(Note that the article calls this "envy" but I prefer "injustice".)
Remember Jesus' parable in which the workers who only work at the very end of the workday get the same amount as those who worked all day? Well, it should be no surprise that the ones who worked all day were upset. Even a dog can detect that kind of injustice.
Just in the case of the parable, it's a graceful injustice, given as a good gift to those who don't deserve it. Being upset may be a natural reaction, but it's still not right!
Wonder what the dogs would think of that?
[This post cannot yet be translated by Google into "woofs" and "barks" for Man's Best Friend, but I expect that capability to happen soon ... ]