Wouldn't the cat eventually learn that nothing happens besides the noise and light? They're rather smart, aren't they? (I've never owned one to be honest.)
The thing is, the vacuum cleaner moves around. I think that is part of the fear factor for cats.
My two were petrified of our shower when it was put in because it's quite noisy, but have both since learned to ignore it. One even sits on the side of the bath watching the water. They still hate the vacuum.
If they figure out that the blender doesn't move around the sideboard, they MAY get used to it, and the owner will end up back at square one. Of course, it goes without saying that every cat is different...
'Better safe than sorry' is normally the smart option in the animal kingdom. There was a story on the news last night about the lionfish which have escaped into the Atlantic. Apparently the native fish don't recognise them as a danger, so they don't swim away and are eaten.
