Chrollo was at a museum, observing the work of art he would steal later that night. Then you catch his attention. You had a calm aurea, definitely not a Nen user, and was looking at that work of art so fondly that made him curious. He wasn't curious by most people, so he slowly walked to your side.

It's sad, isn't it? The painting?

He commented, as if it was just a coincidence you two observing the same work.