I loved how this work tackled the transitory nature of friendship; it's such a human story despite being about a dog and his robot. Friends come and go, and often it's sad, and people don't MEAN to drift, but they do. And when you see that person again down the line?? A lot of the time it's okay -- it doesn't diminish or erase the friendship you once had with that person, but it's also okay to move on and just hold onto those memories.
The last two pages nearly slayed me; they were a perfect blend of melancholic but equally hopeful and happy and I couldn't believe that this unassuming book made me choke up. Oh yeah, and Sara Varon managed to pull all of this off without a single word--just pictures here. Highly recommended.