The Dog-Mind

I often wonder what goes on in my dogs heads as they lay snoring on the sofa.  Not a lot, you might say, but I beg to differ.  Do dogs have a long term memory? Of course they do!  A friend came to visit today who Kizzy hasn't seen for two years and that little black dog went mad running round in circles and grinning like an idiot. She then proceeded to make strange little puppy noises at my friend, who was well impressed at the welcome she got.  It was obvious to both of us that Kizzy not only remembered my friend but was also glad to see her.  If dogs have a long term memory what do you think they dream about?