There's a pass through between our kitchen and living room, seen in the background in this picture. This morning, Drew found paint and drywall dust on the sill in the opening.
Drew called me down to look. He had his suspicions, which were confirmed when I explained that Billy did it. He was chasing a bug (I think), launched himself toward the top of the opening, and sank his claws into the wall ... Where he discovered that he couldn't quite get enough purchase to support his weight, so he slid back down with much claws-on-chalkboard squealing and a certain amount of dust.