Because domesticated animals aren't practicing for anything and would most likely die if they had to live on their own.<quoted text>And just how can you know they are not practicing for the big game? The big game in the animal world is killing other animals to survive. It is a game that must be played and perfected. Now you seem to claim they need no practice and can know their emotions as they practice?
That cat knows there is big bowl of fancy feast waiting. No reason to kill the mouse and then walk away.