Re: Do they do it accidentally or deliberately?
"Why do we have such difficulty in giving other living things credibility for an iota of intelligence?"
Good question! There are a few influences at work here. The greatest blame belongs to Religion, which usually states that we are divine creations in the image of the gods, and animals are dumb vermin-ridden beasts. It's very important for religions to claim humans are separate and special, so there's a default setting of "animals are dumb automatons, we're smart thinking beings not like them".
I lay a fair bit of blame on psychology, ethology and such for perpetuating this attitude. They reflexively dismiss as "anthropomorphizing" any suggestion that an animal might be doing anything we do, or worse, for the same reasons. When it was assumed that humans are a Special Creation that kinda made sense, but not since we know that we're all related.
The newness of Science plays a part as well. When we started looking for natural explanations for the universe (and us), there was a tendency to treat any discovery as the Complete Answer. We're finding out now that most things are far more complex than that first answer we found. That's OK, it's the scientific method at work, moving ever closer to the final truth.
I don't make any distinction between genus Homo and our fellow critters. We're all related from the same origins, and we for sure can share behaviors and motivations. Throw out the preconceptions and you'll see all kinds of animals doing amazing things that nobody much notices or gives them credit for.