She thinks 'Gee...thanks...I learned how to give a blow-job to keep from exploding like an overripe melon'... But of course she can't verbalize it.  Instead, she lets him slide down deeper, doing her best not to gag while struggling slightly to breathe.  Her throat automatically works around the obstruction, and she helps as well.  Soon the muscles surrounding his dick are throbbing quite nicely, delivering quite a bit of pleasure.