Reverse sneezing is the act of trying to suck an irritant backwards through the muzzle, rather than out the nostrils (as in a regular sneeze). Both dogs and cats can do this. The first time you may witness this, it may seem scary to you - the pet will extend its neck and repeatedly suck air in through the nostrils and out through the mouth with the chest and/or abdomen heaving in and out. It is usually a short episode or "fit" lasting 5 - 10 seconds. As bad as it may look - in general these reverse sneezes are harmless.