The blue whale is the largest animal that has ever lived. Ironically, it sustains its massive bulk by eating some of the smallest creatures in the ocean – krill. A foraging whale lunges into a swarm of these shrimp-like animals, accelerating to high speed with its mouth open at a right angle. Pushed back by the rush of water, its mouth expands and its tongue (itself the size of an elephant) inverts to create more room. The whale engulfs up to 110 tonnes of water and any krill within is filtered out and swallowed.

There’s every reason to think that filtering out small prey is an incredibly efficient way of feeding. The largest fish, both living (the whale shark and