Mattie jumped violently at the sound of a voice, said "Asscheek sandwich!" and whipped her head around to look at the man. He was shaking. She was shaking. Yes, a well-aimed rock or two might concuss a living human, but it was rotting flesh that it worked best against and even then there was much less than a guarantee it'd do its job right. She looked down at the weapon. It looked like a machete. She was practically at his mercy, even if she managed to get out her hunting knife. 

"I just need some supplies," she said, trying to keep her voice firm. "I'll be out before you know it." She knew very well that even most living humans had lost the ability to reason when society collapsed.