When you're in the deep, and there's a shark on your tail, who you gonna call? If any dolphins are in the area, call them. There are many documented cases of dolphins saving humans from sharks. The dolphins usually surround the person in danger and escort that person to safety while simultaneously keeping the shark at bay. In such cases, there is safety in numbers, but an individual dolphin will also attack a shark that is threatening its pod or its young. When it's dolphins vs. sharks, it usually comes down to agility vs. ferocity. Despite their seemingly impenetrable carapace, sharks have a soft spot, and fast-swimming dolphins know how to exploit it.

Perhaps the most important difference between sharks and dolphins is that sharks are cold-blooded fish. Dolphins aren't – they are warm-blooded mammals. To be exact, dolphins are cetaceans, like whales and porpoises, and they have to surface periodically to breathe air. Perhaps for this reason, dolphins have evolved horizontal flukes to give them vertical mobility. Sharks, on the other hand, use their gills to extract oxygen from seawater, so they don't have to surface. They have vertical flukes, which give them extra power for horizontal travel but very little vertical mobility. This is a difference that has a big impact. A dolphin, with its bony skeleton for added agility, can literally swim circles around a shark.

Dolphins are natural prey for many species of sharks, including tiger sharks, great white sharks and bull sharks. Most of these fish – and some aren't very large – prey on young dolphins as well as old and infirm ones. When a member of a pod is in danger from a shark, however, the rest of the pod springs to the defense. They will surround the shark, swimming around it in all directions and slapping it with their fins to confuse it. Most sharks end up fleeing, and the technique is so effective that the shark probably won't threaten a dolphin pod again. This is one of the main reasons why sharks are afraid of dolphins, despite their superior strength.

An individual dolphin can take advantage of its speed and rostrum, which is its long, bony snout, to deal a lethal blow to a threatening shark. The dolphin swims underneath the shark and attacks it from below, ramming the soft underbelly of the marauding predator. The blow usually stuns the shark, but it can be strong enough to render it unconscious or even kill it. If two or more dolphins are present, the shark, despite its thick carapace of sandpaper-like scales and incisor-like teeth, doesn't stand a chance. If it can, it usually swims away. Quickly.