"Sstubborn -" Al choked out. Stubborn, sneaky, impossible, teasing Severus! Severus asked, but how! His request became a declaration, a very firm and persuasive statement. One stare down at Al was all it took to turn the tables, to remind Al that he was the one pinned below squirming Severus in a slippery bathwater and that he was nineteen. Nineteen and painfully hard and heavy and hot, with the nineteen-year-old's body and a completely logical response for the situation: fighting arousal on the brink of his own orgasm, just to wait it out every additional second and be able to stare at Severus back.
Their bodies were wrapped around each other in a double-sided knot, like a ginseng root and a mandrake for a Spring Pond Decoction; only Al's movements were far from lazy, born of desperation as he forced himself to unwrap his fingers from his grip on Severus' cock and raised his hand from the water in a wandless, desperate Accio.
Al had to do his best to satisfy at least one out of three previously-established conditions. Books were heavier to summon than bottles and Al really preferred not to get his Kama Sutra wet, so thus, his summoning priorities were clear.