In my work as an editor, I move a lot of words around. And I'd say the word I move most often is the word only.
It ends up in the wrong place more than any other, and I think most writers don't notice (or care). For that matter, I bet most readers don't notice, since they've become so accustomed to seeing it in the wrong place and mentally—subconsciously—putting it in the right place.
Frédéric only speaks French.
No reader would be confused about this sentence. We get it—Frédéric doesn't speak English or Korean or Portuguese. But what this sentence says is that Frédéric only speaks (French). He doesn't eat or dance or work.
The sentence should say:
Frédéric speaks only French.
The word only belongs next to the word it modifies; otherwise, confusion may result. (Many grammarians disagree, arguing that this kind of precision isn't necessary.)