I try not to let it get to me. Some may think that whacking a rat to kill it for snake-food is cruel. Then the same person who says this, goes out and eats a cheeseburger. Ahem, hypocricy!
I do not like to cause suffering, though. I always kill the rat or mouse on the first whack. A mouse being killed by a cat goes through WAY more suffering than the ones I kill!