That's what linguists call it when you inhale while producing speech sounds. It's often said that the only real speech sound that involves really drawing air into the lungs (as opposed to creating lower pressure inside the mouth so that a little air comes in when you release a closure), is the back-channel way of agreeing with somebody in various languages and dialects around the North Sea and Baltic Sea. It sounds like a kind of whispered 'yeah' but you do it while breathing in.
Now, DQ (that's now their official name, right?) has introduced a line of "flamethrower" sandwiches, and when people eating these hamburgers (or chicken sandwiches or whatever) talk, flames shoot out for several feet.* But in one of the DQ ads, to avoid the flames, they talk while inhaling, which is more difficult than you might think for longer stretches. That ad is on YouTube, here, but the owners don't allow it to be posted on elsewhere.
*Just for the record: I only saw this on the television ads for this product, but of course assume it must be true in real life. I'm not willing to actually eat at DQ to test or even observe this effect.