I liked how he told Arya that he had to have a name for the person she wanted him to kill--she told him to kill the one who doing the torturing, and he said "a man must have a name,' so she said he was called the Tickler, and Jaquen said that was enough. It's like a part of a rough code or something, he'll kill people, but they have to be named, or at least nicknamed, like the Tickler.
He may have just wanted to clarify exactly what target she meant. Wouldn't want to kill the wrong person. oops...
My guess is that Jaqen is
Edited by TWoP Dietrich, May 6, 2012 @ 10:56 AM.
Added spoiler tags