Why does a housecat (or other predator) play with it's food before killing and eating it? Does it make the food taste better?
Animal Planet is quoting researcher Dennis C. Turner who claims this is an instinct which is supposed to tire the prey:


  Cats, rather, wear down prey to avoid sustaining injuries. They're motivated by self-preservation, just like most other animals, and they know what could happen if they aren't careful. Mice and rats, for example, can deliver nasty bites that can cause injury or spread disease. Birds, for their part, are able to scratch and peck. So, what's a cat to do? Rather than playing with their prey for amusement, cats tire out their victims to the point where they're too worn down to fight back. And after that, the cats will feel better, and safer, about finishing them off, according to researcher Dennis C. Turner. So while it might look like a display of cruelty, a cat playing with its prey is just an (admittedly harsh) example of animal instinct in action [1].


Karen B. London (animal behaviorist) agrees:


  Actually, the way that cats let go of and then recapture their prey is not a way for them to have fun, but rather a way for the cats to protect themselves from serious injury. Cats kill their prey by breaking the spinal cord with a strong bite to the neck. If a cat must let go of the animal in order to grab it on the neck, that cat is risking escape or retaliation by their prey [2].


Playing (not only with prey) also gives cats experience and improves their ability to make judgments [3].



References:


Animal Planet. Why do cats play with their prey? Available from http://curiosity.discovery.com/question/why-cats-play-with-prey (accessed 27.07.2014)
Karen B. London, Ph.D.. London Zoo: Why do cats play with their food? Available from http://azdailysun.com/lifestyles/pets/london-zoo-why-do-cats-play-with-their-food/article_46a97775-232d-5e56-b0ea-dd1c8782b062.html (acessed 27.07.2014)
Perfect Paws. Predatory Behavior of Cats. Available from http://www.perfectpaws.com/help3.html#.U9TLpON_tJk (accessed 27.07.2014)