I'm taking a survey right now about pet products. Most of it is just the usual guff; expensive toys and treats for the sort of morons who think their pets are human. Then I came across a proposed product that made me stop, sputter, and declare: "OH, NO they didn't."
It's a dog treat that supposedly offers health benefits, specifically noting that it will provide your dog with vitamin C.
For those of you who haven't quite kept up to date on your biology, vitamin C (or ascorbic acid) is a chemical required in trace amounts by all humans lest we suffer from scurvy.
Dogs do not need vitamin C.
Because dogs, like most animals, can synthesise vitamin C. The only animals who need dietary vitamin C are those who primarily eat fruit which is laden with the stuff, rendering the genes for it unnecessary and thus no longer conserved by natural selection. And humans, who are descended from such a species.