Left: Flounder in Italy (picture by tropposnello)
Right: Flounder in Brazil (by MLyra)
Mimetism is the way some animals avoid predators by imitating natural elements like the color of the environment they live.
Flounders have stains in their bodies that mimic the soil they live.
Two examples of how precise they are.
There are other forms of camouflages like "playing dead".
Click to enlarge the pictures. It took me a while to understand the left picture.