I can see why a mirror might be confusing to a cat. It can stump a chameleon, a dog, or a hamster, too. But half a lemon? Why should that be cause for great caution? What does a cat think about a piece of lemon?
I love it when kittens first learn how to arch their backs, puff their tails, and hop around sideways–heap big threat display! Pretend to be scared when they do it.