We have this routine with my cat Ingrid where we plop her in this aquarium with a lid on it & start the gas going. She hisses a little at first, because she's angry, but after a few minutes she settles down, tucks in her paws, starts blinking and eventually puts her head down. It takes just a little more and then we can take her out.

But we have to keep her muzzle in this cone; her tongue hangs out & she dozes. My vet is very cautious with the gas (and I'm glad of it); she usually has to turn it up slightly, because Ingrid will respond to my voice, try to get her head out of the cone, maybe begin to growl just a little.

Otherwise there's simply no way they can examine her. She will NOT allow it. All the fear that she has of that place (the odors & chemical traces that tell her many animals have been there & some have suffered pain there & some have died there) translates into rage. She'll even let me have it if we don't knock her out.

This from a kitty who loves to have her belly rubbed, will let me bathe her in the tub, and even puts up with being rinsed under running water!