There are two kinds of domestic cats - those who have always been domestic, and ruthless killers.  A few months ago, I took in a ruthless killer.  I named her Polly.  She was sweet, malnourished, and calm.  Once she realized I would replenish her food source, she sort of started eating and only stopped to sleep or poop.  Polly now weighs a good 15 pounds.  Her weight increased 500% over the course of three months.  Once Polly realized I was not going to harm her, she started trying to assassinate me.  (I think she wants my Super Nintendo.)  She does this thing where she crouches around the corner of the bathroom door, and when I walk out, she jumps forward at me with her arms outstretched and her claws reaching.  She rarely misses.  Once Polly caught up on missed sleep from living on the streets and warding off wild ‘coons, she took up slam dancing and runs into things at high speeds at 3am.  The good news is that I have not seen a live bug since taking her in.  She sort of bats at her prey with her paw until she gets a claw hooked on the body, and then she bites at the bug stuck to her paw, and then she tosses the bug down to play with it some more.  She can draw out the kill for a good hour before she gets hungry enough to eat it.  And she always eats her prey.  Always.