All Mammals Breathe Air!

A: "Cats breathe air."
B: "ALL mammals breathe air!"

     B's statement is true, but unhelpful. It is best understood as a snarky way of saying, "I already know that." The snark is understandable if we assume that A's intention is to inform B of something new, because it's kind of insulting to be presumed not to already know that cats breathe air. Everyone knows that!
     Yes, everyone knows that. And everyone knows that everyone knows that, so it's equally insulting to presume that A doesn't already know that B knows cats breathe air.  So when someone tells you that cats breathe air, they're probably not informing you, but reminding you, calling your attention to one particular piece of common knowledge because it is immediately relevant to the situation at hand. It's one thing to know, in the abstract, that all mammals are air-breathers, but if you've forgotten to punch some holes in that cardboard box before packing Mr. Fluffy into it for a trip to the vet, it's not clear that you've fully grasped the implications of that knowledge.
     Or maybe B is misreading A's statement to mean that only cats breathe air. This is even worse; B is not just assuming that A condescendingly underestimates B's grasp of common knowledge, but that A is shockingly wrong about the common knowledge itself. One would have to be quite perversely deluded indeed to believe that dogs and deer and humans and horses don't need to breathe air, and yet B is presuming that A is just that stupid.

     In both cases, B is essentially attacking a straw man, creating a weak effigy of A's statement to attack rather than making a good faith effort to understand what A actually means. By making the argument about a perceived insult to B's intelligence, B is trying to avoid engaging with the initial statement, which is irrefutably true and actually reinforced by restating the general claim about all mammals. But not all mammals are about to be transported to the vet in a sealed cardboard box; the fact that cats, and this cat in particular, need air is the point that B is obtusely sidestepping, with potentially disastrous consequences for Mr. Fluffy.