You stop as soon as you enter the cage. You realise your mistake as the door closes behind you. You're trapped!
You look around your cage. There's a kangaroo here, and the place seems to be modelled after an Australian outback. But suddenly, new smells flow into your nose. You're attracted to this kangaroo... You notice a pouch, signifying that she is female. She smells you as well. She turns her back to you, and crouches down to give you a look at her kangaroo vagina.
You feel hypnotised, as your penis swells and becomes erect. But it isn't a human penis. It is now a kangaroo's. The same has happened to your balls as they grew a fine layer of fur, and the semen inside changed from human to kangaroo.
You shake off your shoes, and pull off your trousers, and walk over to the kangaroo. You wrap your arms around her as you hunch over, getting even more excited by the minute. You push your dick into her, as you feel an onslaught of changes coming.
Your legs become extremely powerful and muscular, and grow bron fur all over. You thrust again into your mate.
Your face grows into a muzzle, and your ears push upwards. Fur now covers your whole body. You thrust even further into her.
Your chest barrels out, and you grow a long tail. Your arms are now weak compared to your legs. You thrust again.
Your eyes blacken over. You thrust one last time, as your warm cum goes deep inside her. Your kangaroo sperm would soon pierce your mate's egg.
The zookeepers watched from afar. You wouldn't be the only kangaroo addition they'd be having soon!