The boy that played Jonah is deaf in real life. He communicated with the cast by using sign language and lip reading.
This is one of the first major Hollywood productions to hire only Deaf actors and actresses to play the Deaf roles in the movie. Previous productions would tend to hire only hearing actors (using the culturally appropriate spelling of Deaf, with a capital D, showing those who identify cultural-linguistically as Deaf).
Final film of Hilary Martyn.