At the end of "Hachi: A Dog's Tale", the old Hachi is shown waiting for Parker outside the train station on what turns out to be the last day of his life. When Parker comes out of the station, the old Hachi is shown lifting his head. But the dog that runs up and meets Parker is the young Hachi.
An explanation might be that Hachi, upon seeing Parker, felt young and energetic once again. But it seems to me that it might have been more poignant if the old Hachi was shown slowly walking down and meeting Parker, who then kneels down and hugs his dog. What does showing the young instead of the old Hachi add to that scene?