Continuity mistake: When Ken reads about Hachi on the newspaper it is visible: " Hachiko looks for professor seven years after he died of a heart attack", but in the next scene with the dog in front of him the subtitles show: "It's been a year, hasn't it?" when he speaks in Japanese.
Continuity mistake: In the opening scene the grandson writes Hachiko's name on the blackboard. After a shot of the classroom, we return to the blackboard ("Everyone calls Hachi a mystery dog.") and Hachiko's name has moved on the blackboard. Notice the position of the letter "C" and the bottom of the letter "I". In the final classroom scene Hachiko's name has moved again. (00:00:55 - 01:27:35)hgwalters