There's a Talmudic concept known as "זכין לאדם שלא בפניו," that one can acquire something on behalf of another, even if that other person does not know that this is happening, so long as it's a זכות, a beneficial thing, that people would want. If it's a חוב (something detrimental), or if the other person protests, then we say "אין חבין לאדם אלא בפניו," we only create debt for a person (or do something detrimental) in front of him -- in other words, only with his knowledge/consent. (We also don't let someone use זכין where it's a מקום שהוא חב לאחרים, where others will lose out from this זכין arrangement.)
If some קנין (acquisition) is done through זכין לאדם שלא בפניו, does the מזכה (the guy doing the acquisition) need to be aware of the fact that he is doing something through זכין לאדם שלא בפניו, or is it possible to do something through זכין even without the מזכה being aware that he is doing this?
One possible instance where this would be the case is found on Gitin 11b, where the principle of זכין is used for freeing a slave -- we say that since freeing a slave is a זכות, if a slave-owner gives a גט שחרור ("divorce" document for slaves) to a messenger to deliver to a slave, the slave is free once the document is in the hands of the messenger, because "זכין לאדם שלא בפניו."
However, a friend pointed out that unless we're dealing with an especially astute messenger, he doesn't have in mind to acquire the document on behalf of the slave; he's just thinking to do whatever he's told -- all he knows is that he's bringing a document to somebody.
So can we use the principle of זכין, in a case where the מזכה is not aware that he is using זכין?