Something was different, now. The distorted face in the ripples below, business as usual but for a hideous new set of gashes, betrayed the unmistakable, off feelings in his gut… those he knew better to ignore. "No good deed goes unpunished, Stedman," it had sneered. He risked an idle glance at his half-spent cigarette. The filter was dimpled—noticeably chewed, as was his habit before lighting up—but this time, the paper looked… broken. Fibers peeked out from a hole halfway between a clean puncture and a rough tear. Something had changed. And it was in his mouth.

Sooo unlike the temporary physical changes Cecil undergoes whenever he uses his powers, his chompers are a permanent modification inflicted on him by the devil as punishment for trying to go back on their pact. And he does learn his lesson... he never tries again, especially since he learns the true nature of the consequences of tapping into his abilities at all in the same encounter—including the aphrodisiac-like effect—and instead resolves to simply temper their use going forward... thus making the devil wait as long as possible on him. (There's a pipeline here: ever-present temptation to wield useful, otherworldly abilities -> addiction to power -> higher chance of engaging in dangerous shit that gets the user killed)