Muzan puts a lot of effort into his research, holding his hair and trying to remain patient while pulling his own hair or even digging his nail into his arms to calm himself down, until he heard a sound coming from above his head.

pop

Muzan froze at the sound he felt something move on the top of his head and placed his hands there. To realize he has cat ears and a cat tail wagging behind him.

-"What the fuck?"-

he said to himself while processing what had just happened.