Weird question, I know :P
But it stems from the bit about cats not being able to taste sweet things, because their evolution went a certain route over another. Other animals can taste more flavors, and we're one of them. But are there more flavors we're unable to taste? What would they be?
This is also similar to vision, where some animals see less colors than we do, but birds can see more than us, even UV light. It's fascinating to think about, but kind of hard to imagine, when we're unable to see or taste something it makes it almost intrinsically unimaginable to us. (Can you imagine a color outside the ones you know?)