As he watched Tom's ever swelling body, looking less human by the second, that ring of jealously came through and he found a pig vial in his hand and uncorked soon enough. Downing it without another thought, Matt was already tenting in his pants as the warm musky fluid went down into him.
"What you choo-SWEEEEEEE-se?" Tom managed, every thing below his neck entirely that of a 700 lbs breeding sow, down to the swollen sex in heat and leaking pisshole.
Matt worried for a moment that he had done something wrong, with no changes apparent. Then in a rush he was dizzy and his bowels churned for a moment before pig shit filled his pants and he fell to his hands and knees. As he did, his swelling ass burst through his pants and revealed and already fatty ass with a pig's asshole and swelling boar's balls beneath.
Matt snorted, his body jerking as he orgasmed the last of his human seed. Every pulse caused his ears to grow out and fingers to merge a bit more. Noticing the latter, Matt turned and mounted Tom.
"I chose you," Matt snorted, his movements shrinking legs and fattening belly causing his pants to shred and reveal his already corkscrewing cock. Unknowing he had just sealed Tom's fate, his body changing completely, and permanently, into a pig. With every thrust, Matt brought himself closer to a similar end the moment he came as became a boar. Matt did not seemed almost determined to join in Tom is squalor as his pace, and therefore changes, quickened.