Ramsay calling Theon "Reek" when that was supposed to be the persona he used to infiltrate Theon's group...
Spoiler
You didn't get to book 5, didn't you? Because yeah they skipped the part about Ramsay going undercover but he DOES call Theon Reek... Not wanting to spoil or anything.
I get where you're coming from, but I find it only normal that they're mixing some already known characters instead of introducing tons of new ones. Non book-readers are already mixed up enough as it is!