At first, Jakob felt nothing and saw nothing out of the ordinary. Then, one wall turned into a mirror, and he turned to face it. He felt his pants become a bit looser, his shirt baggier. When he looked in the mirror, he saw himself shrinking, his face growing more child-like, the moustache he was starting to grow fading away to nothing. When it stopped, he looked like he had when he was five—short, skinny, very blond hair, blue eyes, very pale skin—albeit in the clothes of his 14-year-old self. His pants and boxer-briefs were down at his feet, being way too big for him. His shirt covered up his whole body and almost all of his legs, but was rather loose on his shoulders, being so big on a little kid. His feet would easily slip out of the shoes and socks.
A door opened, and one of the scientists, not the one who had spoken, walked in. She was carrying a little kid's set of clothes: jeans, socks, shoes, a t-shirt, a jacket, briefs, all sized for the five-year-old version of him. He tried to run around her to the door, but his shoes were way too big, and he tripped and fell over before he even took a step. She pulled off his shirt, him fighting to keep it on. He saw that his cock had shrunk to the size that it had been when he was a little kid. The woman tried to slide the kid-sized shirt on him. He struggled so much she had to get a second scientist, a man, to hold him still while she put his new clothes on and his old clothes into his backpack. The man picked up Jakob and carried him, crying and pounding on the man's back, into a corridor, the woman carrying his backpack behind them.
Jakob swung his arm around and hit the man in the nose. The man yelled out in surprise and dropped Jakob. Jakob hit the man in the balls and ran off to the end of the corridor. He opened the door to outside and ran through, but the woman tackled him and dragged him back into the building by the back of his shirt. "Subject #247! Behave!" she shouted angrily. Jakob had seen people walking around outside between the buildings, but he hadn't seen what they looked like.
"Just let me go! Let me change back! I don't want to be a little kid again!" Jakob yelled back. He tried grabbing at objects on the corridor's sides—tables, chairs, garbage cans, open doors—to try to stop being dragged, but he couldn't get a grip. The one time he did get a good grip, the man slapped Jakob's hands until he let go because of the pain.
Eventually, the woman came to a closed door. She put down Jakob, and the man picked him up by Jakob's upper arms so that he couldn't do anything but hang. The woman got some keys out and unlocked and opened the door. The man threw Jakob inside and then threw Jakob's bag in after him. After Jakob had been thrown in, he'd started to get up, but the bag knocked him flat again.
The man slammed and locked the door from the corridor side, the woman next to him, leaving Jakob in the room.