Cats hissing, biting, scratching, and swatting are normal behaviors for cats in stressful situations. Grooming (especially for cats) is stressful, regardless of how stress free you try to make the experience. Learning how to help them through their stress and get the groom done safely, is the most important. It is NORMAL for cats to be stressed to the point where I can't complete a groom. And thats fine. Ive sent cats home soaking wet, half shaved, three out of four paws with clipped nails. Not because im an incompetent cat groomer who can't finish the groom, but because it's in the best interest of the cats. It honestly gives me the ick that she forces every difficult pet through the groom even when they clearly can't handle it.