He does hear the quiet approach, but does not feel the need to immediately react to it until he's actually addressed. This is a library, after all; other people are going to be perusing the shelves. He looks up from his book and over to the speaker, half turning to face him.

There are a myriad of reasons he may be being addressed. He could simply be in the other's way and need to move over a bit. Perhaps the book he's holding is one which the other needs, in which case he'll be happy to pass it along. Less likely but still possible is that the library is closing and that he's about to be asked to leave, which would be disappointing but presents no actual problem, or maybe he's been mistaken for a staff member and is about to be asked for assistance. Not that he thinks that is very likely. Non-humans are by far the minority on this particular vessel. He's met one whole handful thus far, and a couple of those have been crew mates, not strangers. Far more likely, given Thane's recent experiences aboard this vessel, is that the man addressing him has never seen an alien before and can't pass up the chance to speak with one.

In any event, he's sure to find out momentarily what the stranger needs of him.

"Yes?"