What’s the best present your dog ever brought you? Mine is the rock pictured here. Jana pulled it out of Lolo Creek at Fort Fizzle, one of our favorite spots to spend a hot summer afternoon. It joins this one:

Jana pulled it out of the same swimming hole last summer.

Does Jana know that hearts have a special meaning to humans? Do dogs use symbols to communicate the way humans do?

Those questions are not as farfetched as they might sound.

Jana loves hunting for rocks in the water, and she often pulls them out to collect onshore or to hand to me for safekeeping. She’s pretty selective about the ones she picks up.

She pokes her head under water, holding her breath as she looks for the perfect rock. Once she’s selected a rock, she lifts her head out and works the rock loose with her paws, then puts her head under water and grabs it. Some of them are huge for a 60-pound dog to carry, weighing a two  pounds or more. Sometimes, I throw one back. And she pulls it out again, often giving me a disgusted look in the process.

They are not all heart-shaped, of course. This stretch of river offers her a large selection of rocks in many sizes, shapes, and weights. Yet many of the rocks Jana chooses are triangular or have an elongated shape and rounded corners.

I can’t help wondering why Jana seems to prefer heart-shaped rocks. Is she sending an intentional message?

Dogs, like humans, regularly  use symbols to communicate with their human and canine friends. Many dogs, for example, bring a leash or guide their human to where the leash hangs to ask for a walk. A human donning a certain pair of shoes can trigger a wild dance of delight in other dogs. Play, aggression, and calming signals are part of universal canine-to-canine body language.

Dogs quickly learn to associate specific actions, such as sitting, coming, or lying down with humans’ spoken words, hand signals — and even printed words or pictures.

But dogs’ abilities go far beyond understanding simple concepts and associations. Studies in canine cognition labs around the world constantly expand our knowledge of how dogs understand high-level concepts.

Dogs have shown that they recognize people in photos and can differentiate between photos of dogs and other creatures. They even associate the sound of a growl with a photo of an  appropriate-sized dog who might make such a sound, looking at a photo of a large dog upon hearing a deep, big-dog growl, for example.

Dogs also learn to associate pictures with concepts. I’ve taught dogs to respond to flashcards printed with words or stick figure dogs showing specific behaviors  (sit, down, speak, etc.). And a researcher in Florida, Dr. Lauren Highfill, recently did a study where dogs learned to ask for their preferred reward by choosing the corresponding picture. They first learned to associate a food reward with one picture, a toy with another, etc. Dr. Highfill even had a “surprise” reward category that allowed dogs to ask for an unknown reward. Some dogs consistently chose to be surprised, while others always asked for their favorite.

So, back to the heart-shaped rocks. I haven’t intentionally taught Jana any specific association with hearts, but she has seen me collecting (much smaller) heart-shaped rocks on our walks together on many different beaches. Maybe she just knows that the symbol is, for whatever reason, meaningful to me.

Jana is very bright and perceptive. Even so, it’s a bit of a stretch to think that she has somehow picked up on the idea that, in human culture, the heart shape stands for an expression of love. It’s not as much of a stretch to think that a watchful dog knows what pleases her human partner and enjoys finding ways to do that. Whatever her reasons, the heart-shaped rocks are gifts from Jana that I will always treasure.