A story I came across this morning.
I personally doubt that most(any?) animals can think abstractly to form communication more complex than 'Polly wants a cracker'.

But if the test is simply to express desire or recognition. I think anyone who's ever owned a dog wouldn't doubt they can express themselves. It's just that they generally are more aware of actions, emotions and tone than individual words. Ha, ha.

I imagine that the trick is to find ways that code 'thoughts' to fit into their worldviews. We've never had a dog that didn't understand a guttural 'uh-uh-uh' the first try.

For years I wondered why parrots liked hot peppers so much until I realized it was their sense of taste. Peppers are a treat they can actually taste.