Humans.

Cat-Man
Once, a guy was walking down a dark street in his hometown, and to shorten the route, he decided to go through the backyards. As he passed by some old barracks, he suddenly heard a quiet, barely audible purr. Not paying much attention to it, the guy continued on his way, venturing deeper into the wooden structures. He was lost in thought when he heard a growl behind him, and the guy lost consciousness.
He woke up in the morning on the ground, freezing. He started walking home, but halfway there, he was stopped by the police. At the police station, they asked him for his documents and other information. Suddenly, the guy felt the urge to go to the bathroom. There, he was overcome by a sudden wave of nausea.
Ten minutes later, the guy woke up on the floor of the room where the police had taken him. Around him lay bloodied bodies. The guy felt something strange on his head. It was cat ears, and a cat tail was wagging behind him.
The guy, frightened, ran into the forest. It is still unknown what happened to him there.