Cali showed her entrepreneurial spirit this week when she decided to buy a tennis ball. Cali adores tennis balls. She loves chasing them, holding them, drooling on them. She especially loves getting one really wet and drooly and then rolling it in the dirt she’s carefully prepared by digging a new hole in the yard. She then tries to sneak it into the living room. She’s not allowed to have tennis balls in the house.

I also like tennis balls. When my shoulders feel stiff and sore, I use a tennis ball to loosen the muscle cramp. I learned this trick from Jana, who loved to position a tennis ball under her shoulder and then roll it down the length of her spine while wriggling on her back. My yoga teacher advised using a tennis ball for this as well. There are two ways for people to do this: lying on your back on the floor, with the ball under your shoulder; or standing against a wall with the tennis ball pinned between your shoulder and the wall. Both work. The problem with the floor version, I have found, is that Cali cannot resist temptation, and she tries to steal the ball from under my shoulder. I end up with no tennis ball and a lot of drool on my neck. So I use the wall method.

The other day, there I was, leaning into the tennis ball. Cali was on her bed, watching intently.I think that part of the appeal for Cali is the “breaking the rules” aspect of getting her teeth on a tennis ball inside. She got up, rooted around in the blankets a bit, and found her Kong. Cali has two Kongs, and at the time I was working on the tennis ball, I knew that one was empty and one had a big chunk of a biscuit inside.

Now, Cali has only recently become a fan of Kongs. Jana was an early Kong addict, and by the time Jana was about 6 months old, there was nothing that I could pack into a Kong that she couldn’t devour in less than 30 seconds, leaving the Kong sparkling clean. But as long as Jana was on the scene, I could not give Cali a Kong. Cali is more leisurely in her approach to Kongs. She’ll work at it for a few minutes, get some of the food out, then abandon it. A few hours later, she’ll find it and work some more. It’s more of an all-day snack than a quick nosh. She’s also more likely to dribble bits of whatever is in the Kong onto the floor, the carpet, her bed … Jana would not let a drop or a crumb escape.

Cali picked up one of her Kongs, walked over to me, and sat. She looked at the shoulder where the tennis ball was, then looked me in the eyes. Back to the shoulder, back to the eyes. Then, still holding the Kong in her mouth, she poked her nose at me a few times, looking me right in the eyes. Oh, I said, are you offering me that Kong? I held out my hand. She placed the Kong in my hand and looked at the tennis ball shoulder again. I handed her the tennis ball. Purchase complete, Cali walked back to her bed, smiling.

I looked at my newly purchased Kong and discovered that it was the one with the biscuit. I pulled the biscuit out and called Cali back to me. She came, leaving her new purchase safely on her bed.

You’ve overpaid, sweetie, I told her. Here’s your change. She accepted her change, ate it, and returned to her tennis ball.

Dog trainers know that the dog gets to decide what a worthy reward is for any task. Cali is more obsessed with tennis balls (and less obsessed with food) than any other Lab or golden retriever that I’ve worked with. But she knows what she values and how to get it. She also knows that a Kong has value, and that one with food is worth more than one without. She doesn’t seem to understand scarcity and how it should affect value, though; we have lots and lots of tennis balls, but only two Kongs. To her, a tennis ball clearly has more value than even a Kong-with-snack, even though one is scarce and the other is common.

Or maybe the joke’s on me: She might also know that she’ll get the Kong back, filled with biscuits, each morning when I head out the door. So it’s not a scarce resource after all.

Now really, who’s the smart one here?