I finally caught Oscar in action, and it was a total accident. Of course. He was frittering around the front door this morning after I took out the trash and spotted what he thought was a bug on the wall. Spoiler: it was not a bug.
His prey was actually a bump of texture under the paint. He goes after these bumps often, along with light switches, which reminds me of his beloved black and white predecessor. Wolfie was also a hunter of wall bumps and light switches, so it makes my heart happy to see the tradition continue.