There's a study that shows that studies of cats' DNA prove they can't form a receptor for sweetness. Somewhere back in antiquity what began as a mutation has developed into a dominant strain, and now,
no cats can taste sweetness.
Here's a link to the Los Angeles Times article, "Cats Lack a Sweet Tooth, Study Says" -
http://articles.latimes.com/2005/jul/25/science/sci-catsweet25Scientists say they have unearthed the reason for the feline's utter indifference toward sweet-tasting goodies: The gene for its sweet-taste receptor is riddled with errors and does not work.
The research, to be published today in the journal Public Library of Science Genetics, was conducted by scientists at the Monell Chemical Senses Center in Philadelphia and the Waltham Centre for Pet Nutrition in Britain.
Previous studies have shown that cats don't care for sugar.My post raised the question whether cats' famously cool demeanor may result from having a narrow emotional range. It's not that they're better able to manage their emotions; they just don't feel things. There's nothing to manage. Cats enjoy playing with mice but it's a mistake to call that a cruel streak. They're just not capable of cruelty. I'm not sure what has been caused a cat's "smile" really is that. That could be just human projection.