Letting the two boys' hands grasp together, you manage to soften your surface, Mike passing through it. Once he's out Luke lets out a sigh of relief, but the only sounds that come out of Mike are more "MMPH"s, as his entire body is coated in a thin layer of your transparent purple rubber. They both start tearing at it, trying to rip it off of him while it tightens around him, getting harder and harder to pull away from his skin. Soon, Mike starts grabbing at his face, trying to signal that he can't breathe, and in a panic jams one of his hands into his mouth, finally managing to breach the rubber and giving him a chance to take a breath. This was just what you'd been hoping for.
Mike gasps for air, swallowing it in the way a man who hasn't had anything to drink for days swallows water. He takes a few deep breaths, starting to relax, but just as he inhales particularly deeply the rubber seals around his mouth again. Instinctively, he screams, the air pouring from his lungs and out into the inflatable coating, which soon starts to puff out. While Luke starts to back away, completely freaked out by the whole situation, Mike's screams cause the air to push out the rubber in front of his face into a muzzle, and with the rubber being so skintight his own flesh seems to follow beneath it, matching the movement and shape of the purple rubber as it extends into a cartoonish, balloon-like fox's snout. As the growth ends, the rubber peels away from the mouth on his newly formed muzzle, once again giving him a chance to breathe in. This time, rather than waiting until he's exhaled, the air that enters his body seems to inflate him directly, a balloon tail beginning to snake its way out of his hindquarters. With every inhalation, the tail grows, until soon it's large, puffy, and luxurious.
Luke, mortified as his friend's changes continue, starts screaming loudly. Worried that someone might actually hear him and spoil your fun, you slowly roll over him, catching him off guard as you pull him into yourself. His screams are soon muffled, and he quickly stops caring about his friend (who's just gained a cute pair of fox ears, and is still struggling vainly to get the rubber off) and starts worrying about his own plight, trapped in a rubber ball. He scratches and scrapes at your surface, but you only delight in the sensation of his hands pushing and prodding at your surface. After a while, he stops, just in time to see his friend starting to shrink away. He once again tries to scream for help, or for something to stop what's happening, but he's powerless as Mike's body slowly loses its substance, the flesh beneath the rubber seeming to fade into transparent air, the still not entirely fox-like shape losing what human qualities remain, and all the details leaving him until all that's left is a purple fox balloon not unlike the one you bought earlier today.
Now finished with Mike, you turn your attention to Luke, who continues frantically struggling to escape you. You could just turn him into another fox balloon, but then again, you've got some free time. Maybe you should have some REAL fun with this one.