David's right index- and middlefinger were still pushing in and out of his (her?) moist vagina. His... her other hand was massaging her breasts' hardened nipples and her moans were slowly changing into canine-like whimpers. Her ears slowly grew to a pointed shape.
Fully entranced in the incredible and formerly unknown lust of heat and while feeling her wet pussies juices all over her pushing fingers, she did not notice that Jeff was slowly creeping nearer...
Jeff's body was nearly covered in red-brown fur now and his hands and feet were slowly turning into paws. His face had pushed out into a wolves' muzzle and sharp teeth glistened in his maw. A bushy tail slowly grew out of his tailbone while his mind got flooded with canine instincts.
Even if Jeff's warped body resembled a human being at least in a slight way up to this point, his penis had changed shape completely. The huge, pink and slick canine cock, which was still fully grown out of it's sheath, proudly stated Jeff's will and ability to procreate. Thick blobs of precum oozed out of the cock's tip and dropped to the room's carpet floor.
Jeff's canine nose inhaled the incredible attractive scent the other being in the room radiated. It was a female, a bitch, and Jeff's new set of thoughts told him that he was ready to mate with her as she was ready to be mated. His cock hurt as it screamed for release inside this marvelous bitch's pussy.