How does the boy try to get the attention of the young horse in the pasture?

Albert gets Joey's attention by using their special whistle.

On the way back to the farm he would allow me to follow on at my own speed, and I learnt to come at his whistle, not out of obedience but because I always wanted to be with him. His whistle imitated the stuttering call of an owl – it was a call I never refused and I would never forget.