Jack gets a horrible, horrible headache. He clutches his head and when he withdraws his hands and looks at them, he notices that his fingers are pointing, starting to become claws. His ears and canine teeth also start pointing
Jack gets a bellyache. He feel like he's about to fall over, but he stay upright. Jack pulls up the shirt, and sees that his belly and the lower regions of his chest have become covered with fur. He takes the shirt off. The fur is white on his front, but yellow-gold everywhere else. There are black spots dotted all over. His nose and mouth have stretched out and start to become a muzzle. His nose, and also your eyes, seem more catlike. His ears have become furred over with the yellowish-golden fur.
The fur spreads upwards onto his chest, same pattern as before. His face has now become fully akin to a cheetah, Muzzle and all.
The fur now spreads to his pelvis. Jack takes off his pants and sees his testicles receding, internalizing. His penis follows suit, and the areas they once were in get covered with fur.
The fur spreads down to his legs, reforming them so that he's standing digitigrade.
At this point, his tail is at full length.
His feet get overtaken by fur. They reform into paws.
The fur now spreads to his arms, changing them to be more lithe.
The changes concentrate in Jack's hands. They get covered with fur. His hands are now an odd mix between hands and paws.
Jack feels the transformations fade and figures out he has become an anthro cheetah.