One of the most dangerous and downright vicious species on Earth is the wild aquatic extractor fan, which roams coral reefs, attacking anything edible. They have been known to hunt in packs, chopping creatures as formidable as tiger sharks to shreds with their whirling blades. Their land-based cousins, on the other hand, are extremely docile. They live in small, air-conditioned burrows by river-banks in southern Europe and some parts of Polynesia, and can be easily trained to sit on windows for their entire lives, feeding off airborne particles of water and mildew, and the occasional unwary finger.