In the zoo of programming languages there are two cute yet rather misbehaved animals, typically found in the Dynamic Languages section: the Duck Typing and the Monkey Patching. The Duck Typing is hardly seen. You hear a “quack!”, but you can’t easily tell if it’s coming from an actual duck, a parrot, or a recording. Monkey Patching, like the name suggests, patches any existing creature to change their behavior. It can even make a dog quack! While these two animals bring lots of joy, they are also quite dangerous when used in the wild, as they can bring unexpected behavior to the rest of the creatures. Crystal is a rarity in the Static Languages section that has Duck Typing and Monkey Patching. Given the strong —yet barely visible— fences of types, it manages to properly contain these beasts. In this talk I will present Crystal and provide a glimpse at how it manages to feel so dynamic.