That pile of crap he'd jumped down onto hadn't been as stable as it had originally looked. He'd made more noise than he had planned on, and promptly gave a quick and cautious look around to make sure his ass was still safe.
The shuffling hookers were still on the corner. Check. Almost headless guy near the stop sign seemed to still be in a world of his own. Check. And another quick look back toward the pharmacy-- aand the coast appeared to be clear. He hoped.
So he needed to head toward the back to find out if the place still had any antibiotics. He didn't know a whole lot about prescription drugs, but maybe he could just fill the bag with bottles that looked like they might be of use, and in the process, hopefully he would find some Amoxicillin or Penicillin or.. something.
He would have never noticed that he wasn't alone if it hadn't been for that creaking door. And that stopped him in his tracks. Hesitating a moment, he gave another quick glance around the place from where he stood, and then cut his eyes back toward the back of the store-- that's where the noise had come from. Reaching for his gun, he pulled it from it's holster that was hidden beneath his coat, and slowly started to make his way toward one of the side walls. That way he could keep his shoulder to it, and give himself a clear path if anything came at him.
Pausing, O'Brien kept his eyes on the back of the store, only giving a brief look toward the shelf, and then back, so he knew exactly where to reach for the box of Batman band-aids. None of that Hello Kitty nonsense. Reaching back to tuck the box into his backpack, he continued toward the back.
He supposed he could call out-- but that only riled up the infected, and he didn't need that. He continued along the wall, toward the only door that he could see, and it just so happened to be ajar, so he could only assume it was the one in question. Someone-- or more likely, something was just on the other side of it, and he didn't intend to let it attack. Boom, one shot in the head before it could even lunge--That was all it would take.
Catching movement out of the corner of his eye, he quickly turned to focus on it, his gun aimed and at the ready as he started to make his way around the shelving.