[Slater is sitting back at the library's desk, reading
Extraordinary Popular Delusions and the Madness of Crowds by Charles Mackay. He's just at the start of the book with a 'I haven't decided whether or not I'm taking this book seriously' look on his face, although he's fairly absorbed in it.
His job is to sign out books. He does this with a leery eye and and unimpressed look: the kind that anyone with previous dealing with police-like services is going to interpret as the look a cell-sergeant gives you before he hands back your belongings and lets you back into the wild world. You'll be back is a threat a little out of place in a library, but the implication behind it reminds the same. You'll be back here because you've failed: either at graduation or graduating someone else.
If he can get away with it, he'll say nothing to you beyond telling you when it's due back before shoving it in your direction. He continues staring at you as he reaches for his book and sits back. Properly seated, he returns his eyes to the page he left off. Consider yourself dismissed.
If you're the kind to walk out without going through the paperwork, it'll seem to the casual observer that he doesn't notice, such is his interest in his reading, but the more observant among you will notice his eyes flick up and watch you as you leave.
What'll come of that? Well, nothing, unless he can think of way to work to his advantage.]