Did you know animals and birds can communicate with in many ways?
Even bees have patterns of "dancing" in the air to tell others in their hives where to find good nectar.
Many animals can sense things humans can't, such as sounds out of our hearing range or color vision that's different from ours.
Dogs communicate a lot of things to each other through their strong ability to smell things. I'm glad humans don't have to greet each other by sniffing certain body areas as dogs do! Those animals can tell all kinds of information when they sniff where other dogs have left urine. For instance they can sense if the other dog is mature or not, male or female, healthy or not, well fed or not, aggressive or frightened, etc.
A while ago I blogged about a book called How to Speak Dog by Stanley Coren.
Coren doesn't mention smell communication, but explains how dogs communicate by using body language, barking patterns, and intonations. It's amazing how much they can communicate!
That book also talks about cat language, and how cats and dogs often don't get along because some of their body languages mean opposite things. But if they're raised together they can understand each other.
I've told so many people about that book the author ought to pay me a commission. :-)