Sometimes we think sparkly jewels are diamonds, but they are really just glass. Other times we believe that our baseball card is signed by our favorite player, but it is only a copy.
Animals can make copies too.
Some copies are so good that we don't know that they aren't the real thing. Smaller, weaker animals have to imitate stronger animals to stay alive. If insects or other less powerful animals can trick their predators into thinking they are a different animal by the sounds they make, or the colors on their body, they just might survive a little longer. Take a look at these two butterflies. One is a Monarch and very yucky to eat.