You wake with your face pressed against a cold smooth metallic surface. You open your eyes to see a plasticine grate. You're in a large plastic cage. You sit up, self-consciously realizing that you are naked. You reach to cover your morning erection as you look around your new enviroment.
You are surprised both how small and furry your member is when you touch it. You look down to see your naked body is covered in a fine brown-grey fur. Your penis seems to be physically retracting or shrinking back into your body. You notice that your nipples have migrated down your chest toward your belly, and that a longitudinal fold has developed across your abdomen. You suddenly feel a tail pushing you forward, you turn to see a thick furry tail growing out of the base of your spine. Your hands and feet are getting narrower and are elongating. Then you notice the man in the cage next to yours. You recognize his face from yesterday, it's the jogger who passed you just before you met the odd robed man. His changes are more pronounced than yours. He clearly is transforming into a large male kangaroo. His red engorged penis peaks boldly out of his furred shealth. His face elongates into a snout as you watch. Something is making him really horny. He hops madly about his enclosure. Then eying you, he sits back on his tail and kicks the front of his enclosure with both his feet. There is a loud crack, followed by a thud, as the front of his enclosure is broken open and falls to the floor. He is feeling around the front of your enclosure with his tiny roo hands.
Suddenly, you realize that you are holding nothing in your hand, you lift it up to see that your penis has completely vanished. There is a burping noise like air rushing into a newly owned piece of tupper wear. Liquid oozes out of your newly formed vagina. You realize that you are becoming a female kangaroo. Then the musky odor of the male kangaroo hits you. You are smaller than he is, but you rock back on your tail and kick the front of your enclosure once, twice, three times, and it too cracks and falls forward. The whole time the male is hopping eagerly off to one side.