So if something is "anti-ninja" then it would repel ninjas, right? But if it's an anti-ninja repellant, then it would repel anything that repels ninjas, thereby attracting ninjas instead. It's hard to understand so let me put it this way. Let's say you have 4 + (-3). That would obviously be 1 because it's a positive 4 plus something negative. However, if we change that to 4 - (-3) then you have a double negative which results in the answer being 7. Get it?