Downworld

You go to the alley and peer inside. After giving your eyes a minute to adjust to the darkness, you realize there's a guy, around your age, leaning against the wall. He looks like he's in pain. You enter the alley.
"Are you alright?" you ask. The man jerks his head up at the sound of your voice. He grabs his throat and shakes his head no.
"Do you need a doctor or what?" You hold your hand out to the man, and in a flash he has bitten your wrist. You jerk your arm away and yell, "What do you think you're doing?" He looks at you with a strange look, like hunger. What do you do?