Here are 2 words he cannot say:
Soi/Soy (He makes a strange SWAH! sound when this is read. However, this is rectified if the next word starts with the w character. For example, "Soi water" will make him say "Soi" correctly.). If he reads "Enjoy the vacation time!", he will say 'EnjWAH! ...the vacation time!".
Ped (He makes a spitting sound. It is uncertain if it can be rectified.).