This is from my friend West Coast Louis. I had no idea.
"Something you wrote on 3/12 reminded me of a funny thing my sister told me. She works in South Carolina as a vet surgical assistant, and is studying to get qualified as a vet anesthetist. They don't really have vet anesthesiologists, apparently, but it's a job that needs to be done.
"I'm making assumptions about the size of your dog, but it sounds like she's small, as dogs go. My sister was telling me that dogs that size can't be gassed with a mask, so they put them in a clear plastic box and fill it with a mixture of oxygen and anesthetic gas. It takes about 30 seconds for a dog to go to sleep, but before they do, they hallucinate, probably for about 10 seconds or so (don't know if that's what they'd use for a teeth-cleaning, but they do use it for more substantial surgery.)
"As you can imagine, dog hallucinations aren't too complicated, just like dog dreams. Apparently, though, all the hallucinations are kinda similar; dogs start swinging their heads (and eyes) from side to side, watching something going back and forth, and it tells the vets how effective this gas is. My sister says they call this behavior 'Watching Tennis.'"
And dogs love tennis balls, too. I pick up Roxy's and she's rapt. She's got a good little attention span for a quadruped.