"...your muscles." Mike looked at Jeff in surprise. Jeff explained, "You and I both know how strong you are, but you don't look it at all. If I didn't know any better, I would have said you were some pet rat! All I want to do is alter your body so it matches your power, and make you a real mutant monster rat."
Jeff navigated the options until he found two that would come in handy - the 'Muscle' and 'Muscle density' sliders. He clicked both of them, but instead of inputting a value, he also selected 'Continuous Transformation'. When his dad reached a good size, he'd stop it manually. Happy with his choices, Jeff began the transformation without warning.
Mike gasped as he felt a strange feeling overtake him. His body began to swell with muscle, beneath his fur and fat, and he could feel the weight piling onto him. The visible growth was slow, thanks to the 'Muscle Density' option, the two at war with each other as they simultaneously attempted to grow and shrink his muscles at the same time. Even so, Mike could feel every amazing second, the feeling of him growing larger, power rushing into his tiny body with each passing moment.
Soon, muscle began to show through his fur, pulling his skin taught across them. Mike writhed on the floor, using his prehensile tail to feel up every inch of himself as every muscle flexed, growing more and more pronounced. Jeff watched in amazement as his tiny lab rat became a rat bodybuilder in just a few minutes. Thick, round biceps bulged, Mike digging his claws into the ground as his back became valleys of huge muscles. When he threw his head back, he gave his son a good look at his defined 10-pack abs. His legs bulged thicker than Jeff's wrist as they pulled the muscle monster to a standing position.
Now, Mike had certainly grown in size as well, going from just 25 centimetres from tip to tail to a large 60 centimetres. The two-foot rat stood halfway up Jeff's calf, but he was far thicker than it. Every inch of those 60 centimetres was covered in boulders of muscle so defined they could cut rock. Veins pulsed across them, even running down Mike's tail, another monster of pure muscle that coiled and writhed like a snake on the floor behind him. Satisfied with his work, Jeff ended the transformation.
"Wow," was all he managed, as his dad slowly crept towards him. It was intimidating enough with a rat more muscular than any bodybuilder he'd seen on TV, but knowing that rat could also lift his entire body weight with ease was even more terrifying. Mike placed a much larger paw on his leg, just so Jeff could feel its vice-like grip. He let go and thundered over to the scales.
"5kg," Jeff read out in wonderment. "That's over twelve times your previous body weight!"
Mike flexed his body, showing off his rippling muscles as if to say 'Well, this is why'. Jeff grinned. "That's amazing. You're certainly a monster of a rat now. And I reckon you're still stronger than you look."
At that, Mike had to pause. Because while the feeling of his muscles infinitely expanding and contracting was certainly the main attraction of the transformation, he had definitely been growing more powerful. He certainly felt stronger than he was before. But how could that be...
He would have laughed if he could have. Of course, how could his smart son be so stupid? He'd modified Mike's strength in proportion to his body's natural ability. But a normal, ordinary lab rat was pitiful in comparison to a monster rat adorned with kilos of hyper-dense hyper-muscle. And times that by 1,000, well, Mike might well have been a god at that point. He knew he could rip apart cars like they were paper, smash entire houses to the ground, and, with how dense his muscles had become, not suffer a single scratch in return.
However, he wasn't about to tell that to Jeff. He simply flexed again and watched his son coo over his magnificent, monstrous body, and awaited his next transformation.