Mallard ducks seem cute. The males have bright, colourful plumage, and they waddle around endearingly. But it turns out they’re actually quite terrifying. Their penises grow up to 20 centimeters long, and they are incredibly aggressive. They may chase down unwilling females and force them to mate, often in gangs. While it may be a part of the natural order of things for ducks, it’s extremely unpleasant to think about, and ducks during mating season are best avoided.