Neither boy can read until Tito gets a few lessons, but still can't read well, however, when the horse takes them to their mother's grave Ossie, who has not learned to read, asks (at around 1h 18 mins) "Why is my birthday on that stone?"
The horse ranges in color, from gray with darker gray mane and tail, to almost completely white, and a very noticeable braid in his mane disappears and reappears throughout.
The photograph of Mary Riley shown at the beginning is larger and more widely framed (showing much of the front of her caravan) than the "same" picture shown at the end (showing only Mary and her baby in the door).
The dogs used when officials are tracking the boys and the horse through the forest (01:15:00 to 01:17:10) change from crop-eared to natural floppy-eared.
In several shots of Tito and Ossie riding bareback while the horse is galloping, Ossie is represented by a very floppy dummy that's obviously tied and pinned to the stunt rider playing Tito (01:13:44 to 01:14:51).
When the grandfather is arriving at the Towers in his caravan, another man standing in the caravan is clearly visible (at around 59 mins), even though the grandfather's only companions were his dog, his black horse and Tir Na nOg.