Sawyer: How do I know that you didn't just paint an eight on a different rabbit?
Ben: You don't
*Punch*

My first thought during this scene was, of course, that Ben's "You Don't" was part of his mind game - you can't trust those who con you. But the way he replied that Sawyer couldn't know that they didn't paint an eight on a different rabbit - makes me think that the eight wasn't paint, but was the bunny's fur, genetically designed to grow in that pattern. Ben thought: "Of course you don't know - you don't have any idea why that eight is even there."