No, that is not animal cruelty. Dog fighting is animal cruelty. Forgetting to feed one's adorable pet... five times is animal cruelty. Tying those little sandbags to kitten's feet can be classified as animal cruelty, regardless of how completely hysterical it is.

Killing rats is not animal cruelty.
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We kill animals every day for food, and this is not animal cruelty? But killing rats to berid yourself of a pest problem is?