My best reactive target's are large pine cones, thrown up against the dirt backstop. Shoot at the bottom edge of the pine cone --- and they fly as much as 10 feet in the air --- trick is... shoot them while they are still aerial; or rolling down the backstop.
I also like balloons, spinner target's, and live houseflies and yellow jackets crawling on white target paper --- the reactive part --- is the bug splatter on the target paper.
That rifle hanging on the wall of the working class flat or labourer's cottage is the symbol of democracy. It is our job to see that it stays there."
--- George Orwell