Dude. Even dogs get jealous of other dogs. How are we still in a time where we think animals don't have an inner life?
I'm being completely honest here, I believe pigs and cows are just as intelligent as dogs. They're simply limited by their physical bodies and our understanding of their expressions.
But I still won't go vegan.
On an intelligent level I believe it's wrong to inseminate cows so they produce milk, but I still won't stop drinking it. Because I am lazy and comfortable in my ways. And that's what I believe most people are, even if they won't admit to it.
Morality is an artificial instrument of social control that minimizes human wars. Otherwise, all creatures are here to kill and breed.
When asked about causes of our behavior, we readily make up an explanation, and we believe our own explanations completely whether they are true or false. There is a considerable literature demonstrating in an experimental setting how easily the behavior is controlled by the factors that are not consciously perceived, and how it is rationalized post factum in plausible but arbitrary ways. More informally, many fiction writers show characters, for example falling in love and showing that through their behavior, but refusing to admit that they are in love, even when explicitly confronted with the facts.
Of course one can say that an adult human can at least in principle, sometimes, examine what is going on, while a dog is probably much less capable of such complex analysis and is more like a small child. This seems plausible.
Once a friend of our dog came visiting, grabbed his favorite stuffy and happily chewed it in the yard. Which our dog clearly resented.
So he cleaned up the yard and hid all other toys in the house. Usually that's our job - he never bothers to look after his toys.
Then he came out with an old tennis ball, pranced around, played with it, like "Dude, this is the BEST toy EVER invented. An it's mine."
His friend dropped the coveted stuffy and came over to investigate... our dog dropped the ball, grabbed the stuffy and hid it in the house.
His friend was left with a slimy, boring ball.
I really can't think of any other explanation - he knew how to get his stuffy, but also anticipated this trick wouldn't work twice. So the cleanup in advance.
But he showed real intelligence by never doing anything like this in front of us ever again. ;)
It's a small wonder whether the dog did that when the owner was home!
A simpler, somewhat common version is when one dog pretends that there is something interesting outside, so that the other dog would drop the toy and would run to the window hoping to bark at the mailman, while the trickster picks up the left behind toy.
Some dogs actually learn to see through this ruse. It can be very amusing to watch them darting instinctively, then suddenly realizing what is about to happen, returning back to pick up the toy and only then going to the window more leisurely.