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Any time that a cat won't eat for this long, you should be worried. Their systems can't handle a famine and their organs can fail.
If this does not resolve itself soon, you will want to see your vet to rule out a medical reason for the behavior.
He might just be hoping that if he scares you enough, that you will return the new kitty to where he came from! (just kidding)
Let me know if you have more questions for this.