This morning I was listening to a radio discussion about the multi-modal sensing used by dogs. It reminded me of one of our dogs from many years ago (oh boy, geezer reminiscing).

Koa was a pure bred German Shepherd. One of his favorite things were rocks; any rock (larger than a tennis ball) was fine with him. He would pile them up and lay by them, play with them and carry them around in his mouth.

The interesting part of Koa's rock love was his ability to find a rock you picked up and threw. He could find a rock that was thrown into tall weeds and trees, among many other rocks, as far as you could possibly throw it. Sometimes it would take him ten minutes to find that exact rock. He always brought it back to you and dropped it at your feet for another "toss". If you chose to throw a different rock, he would find that one as well. If another person threw a rock he would go find that one and bring it back to that person, too.

One day, I accidentally threw a rock into the river that flows by our property. Much to my surprise Koa swam out into the river and dove under multiple times until he found that exact rock. Underwater rock fetching became a favorite activity.

I assume then that Koa used several senses to find the rocks including:

Sight (seeing what the rock looked like and the direction it was thrown)
Sound (hearing the approximate direction and location where the rock landed)
Smell (smelling the "tosser" of the rock)
Rock sensor (well, no, but it did seem like that sense existed too)