Truthfully.

You notice how uncomfortable the goblin girl is becoming, so you decide to tell her the truth. You are sure that she is no danger to you anyway in her current condition.

"-cough- erhm... You see..." You mutter, trying to find the right way to explain what you did.

"I might have, uuh... inserted a few false memories into your subconcious while you were passed out... sorry?" You raise your pitch at your last spoken word and give her an apologetic smile while shrugging your shoulders. "You see, I have this, weird ability that lets me manipulate an opinion or memory a person has, and, after I saved you from the dwarven skeletons I... wait... what were you doing in that old keep anyway?" You give her a puzzled look.

"Gibbi tell later!" the goblin girl weakly yells, but winces in pain while doing so. "Why human manupu... manipi... maniputate Gibbi's head visions?" She asks, her face having changed to one of confusion.

You sit up straight and try to put on your most sincere voice, "I wanted to make sure that you wouldn't try to kill me when you woke up." You give her a smile and a chuckle. "I am... very far from anything I know, and you are the first living thing I have seen here, so... I thought that if I helped you and you thought I was a friend, then you might help me too?..."