You know what I dislike? Ineffective wormers. You do not want to merely anger parasites, you want to finish them off. I have way too many customers who dose incorrectly, or choose the wrong wormer because they don't know what type of parasite they're dealing with. If your cat has a tapeworm, do not purchase roundworm medication. They are not the same thing. And then, for goodness sakes, do not complain about the ineffectiveness of the wormer because your cat STILL has a tapeworm even though you bought medication, paid real money for it and everything, but it didn't work and they don't make anything like they used to.