Kitty could also be carefully checking for presence of radioactive atoms, Prussic acid, and Geiger counters.
It’s always been my understanding that a cat that stares at you doesn’t trust you. The long, slow blink is a signal that the cat is comfortable around you and feels it doesn’t need to keep its eyes on you every second.
The polite thing to do when given a long, slow blink is to blink right back. You can also defuse a staring contest with a cat-like “comfortable” blink (unless of course you really are up to something and the cat has good reason to remain suspicious).
When my cats stare, they’re just waiting for me to perform the Amazing Can Opening Trick. If they could only learn that one trick, they’d have no use for us monkeys whatsoever.
And yes, I think even Miss Manners would agree that the only polite response to the slow blink is another slow blink.
When a cat stares at you that means they’re trying to locate the precise point on your neck where they can rip out your jugglar vein. Once they’ve spotted it they’re torn between bestowing upon us a quick and relatively painless death, or waiting to see if we’re going to set out some more food for them. Fortunately most cats are fairly patient creatures. Most.