Matt slammed the door open as he ran into the bathroom, shaking the walls and causing Ben to wake up with an animalistic grunt and the Neanderthal was greated by Matt's new half-caveman scent. But there was more to it. Ben knew -or rather his new instincts told him- immediately what was happenin: He was given a chance to get some company, to expand his tribe.
With newly discovered energy he launched himself from the sofa and knuckle-walked towards the bathroom Matt was in.
Matt himself was occupied with overseeing the damage done to him. He had gotten a lot more hair all over his body, was clearly more muscular, and his face had gained some clearly unnatural proportions. His nose was broader, his forehead stuck out like a lighthouse and his eyebrows had suffered a similar fate. The worst thing though was that he had clearly started to produce a stench similar to Ben's, not as strong, but still enough to have him get the strange urge to get down onto his knuckles every time he breathed in.
"If Ben could turn himself into.. that, then we can fix this shit aswell." He thought to himself.
Suddenly Ben grabbed Matt from behind, dragging him back into Matt's room.
"Hey! What are you doing! Get off me!" Matt struggled, hitting Ben who just grunted slightly as Matt hit his muscled chest.
"You be caveman!" Ben replied "It be great! Will be friends!"
It was clear to Matt that Ben had already lost a substantial portion of his former brainpower, especially since he had jacked off. There would be no point in pleading, so he just continued to struggle against his captor.
Ben threw Matt onto the sofa, then himself onto Matt. The caveman rubbed his sweaty body against Matt, ramming his hairy armpit into his face. Matt continued to struggle, screaming at Ben to stop, but to no avail.
As Ben grew erect from his friend rubbing against his member precum started to leak onto Matt's chest. On and around the stain, and wherever Ben's sweat touched Matt (essentially everywhere) hair started to grow once more.
Matt could feel how his brow ridge started to expand over his entire forehead, becoming more pronounced.
As this happened Matt's mind started to cloud over. His body stopped struggling, and soon his thoughts did aswell.
Would it really be that bad to just be sniffing his hairy armpit, jacking off, and eating all day long? No, it would be great! Matt started to actively inhale the musk as he felt his body get even hairier, his mouth broadening as his entire jaw pushed out. His penis grew in size (and hard) from his normal 3 inches soft to 6 inches soft and 10 hard, as he started to drip cum onto himself. He had the urge to grunt, so he did and Ben joined in pleased.
Matt felt his entire body shift, as he shrunk from his former 5'11 down to 5', but gaining more muscles in return, including a hard sixpack hidden under the hair. His arms on the other hand elongated a good 8 inches, his feet stretching themself from size 9 to size 15. He would certainly not be walking straight on both feet with such a physqiue anymore.
All this was accompanied by Matt loosing his mind to his new feral instincts.
Finally Ben released his grip just to see Matt grin with his enormous mouth at him.