What happens when you hire a model to do an actor's job

I've changed the words just enough to not be recognized, without changing the truth of it at all -- this is not exaggeration or hyperbole -- this really happened on a professional set.

Principal actor-who's-a-model-and-not-so-much-an-actor-but-sure-does-look-good-in-the-costume, delivering his lines in the scene for at least the 6th take, probably more like the 10th or 15th when you factor in the different camera setups:

"Trees. Trees trees trees trees trees treestrees. Trees. All we ever talk about is trees. But I'm here today to say 'no more.'  Starting today we will not talk about...............-- [breaking character, calling off] What is it?"

Script supervisor: ".....Trees."