Sammy wasn't sure how long he wanted to wait. But he was definitely sure that he couldn't wait as long as he did with Amy because that was absolutely crazy. He didn't have anything against humans, it was just on his blood. Or was it? All he knew was that the longer he waited, the weaker he got. Either way it doesn't matter because no ignorant human would think a cute fluffy kitten to be a murderer. If he ever got caught, well let's just say it would make one hell of a news break. But even if a stupid human saw Sammy kill,  they would never believe their own stupid eyes. Even if someone did believe their eyes enough to share what they had seen, none of the other stupid humans would believe their story. So as far as Sammy knew, he was safer than any killer could be. And that's the only good luck Sammy would ever have. It would take one hell of a miracle for Sammy to have any further good luck.