Though he'd trusted her up until this point, her demonstrating whatever made her a freak had the reflexes kicking in. There were enough people around that if she wasn't strong enough, they'd cause a scene and he wanted to avoid that. On the other hand, she could be minutely aware of everyone around and knew they didn't pose a threat. So, as bright blue bolts of electricity crackled between her fingers, he moved to pretend like he was going to scratch an itch on his lower back, where the gun was, careful to not his face betray him. When it dissipated into the air with no harm done, he committed to the act, scratching a non-existent itch before bending slightly backwards.
"Alright, Thor," he commented with a smile and a laugh. "I've got to admit, not the freakiest thing I've ever seen." Dean filed the demonstration away, just in case. If he could find out anything about her, or what she was, it could be helpful in the future. The fact that she could have easily killed him but didn't stuck too. He was still slow to give the benefit of the doubt to anything supernatural, but for now, while no one's being roasted alive, he could trust her. A little.
"How long have you had that?" He didn't think my many things out there acquired powers, but since coming across the Men of Letters warehouse, he had started to learn there was a hell of a lot more out there than he'd ever seen or thought of. If she was willing to share, it could help. He just wondered if she could trust him. He had a feeling most things out there learned the name Winchester one way or another. She didn't seem to recognize him, so that was a plus.