Few things get the adrenalin spiking quite like a big brawl, even if you are just a popcorn-guzzling spectator. But if you want the real ultimate fighters you need to look to nature, where champions compete for more than glory: they fight to survive.
The hardest hitters on Earth are highly likely to take you by surprise, and not just because of their speed and skill.
The owners of possibly the fastest punch known to science are marine crustaceans called mantis shrimps. They use specialised forelimbs to strike prey with shocking power. The force is so great that the mantis shrimps tear through the water, creating small implosions that generate heat, light and sound.
Some species have adapted specialised appendages to spear, like a harpoon, while others smash with a club. In captivity, they have been known to break aquarium glass with a single hit.
Many social insects clash by knocking their antennae together
Sheila Patek's laboratory at Duke University in North Carolina specialises in studying fast animal movements. Patek's team has discovered that peacock mantis shrimps can generate a force peaking at nearly 2,500 times their body weight in less than 800 microseconds.
Patek says springs, levers and latches are the key to this amazing ability. Within each mantis shrimp's appendage is a four-bar linkage system that manages force. One link pushes against the next, building up energy before it is unleashed through the harpoon or club segment.
"Much like an archer, the mantis shrimp stores up elastic energy in advance of the strike and releases it with a latch," says Patek.
The shrimps also engage in territorial contests. However, Patek and colleagues describe these encounters as "ritualised sparring" rather than lethal contests. Competing shrimps first size each other up, and only come to blows as a last resort. On the rare occasions that they physically fight, the shrimps first curl up their armoured tailplates, or telsons, to shield their abdomens. The winner is the shrimp that, like Rocky Balboa, can withstand the most hits.
Patek has also studied insects called trap-jaw ants. These insects are named for their mouth parts, which can snap shut on prey astonishingly fast.
Hares often fight duels in spring as the mating season begins
They also brawl to settle disputes, boxing one another with their antennae to determine hierarchy within the nest.
Many social insects clash by knocking their antennae together: the behaviour has been studied in ants, wasps and bees. Touching antennae does not always signal a beatdown: for example, honeybees rapidly touch antennae while exchanging food. But for letting others know who is boss, boxing is key.
In a 2016 study, researchers used high-speed cameras to record four species of trap-jaw ants boxing with their antennae. The Florida native Odontomachus brunneus struck its opponent 41.5 times per second. The team described trap-jaw ants as "the fastest boxers ever recorded".
Among mammals, probably the most famous thumpers are brown hares (Lepus europaeus).
Hares often fight duels in spring as the mating season begins. This is the origin of the phrase "mad as a March hare".
It was once believed that only male hares fought, competing for mates by swiping at their opponent with their front paws. However, modern research has shown that boxing matches are often started by females, who are not yet ready to mate and choose to fight off pushy suitors. Females only have brief windows of fertility, so males must be persistent.
Kangaroos also kick in self-defence, as many unfortunate Australian dog-walkers can attest
In Australia, the bulging biceps of male kangaroos signal more sexually-charged scuffling. A particularly ripped specimen known as Roger resides at the Kangaroo Sanctuary in Alice Springs, and has become a viral hit thanks to his bucket-crushing guns.
According to a 2013 study, the males' over-developed forelimb muscles are a result of sexual selection. Male kangaroos slap and grapple one another to settle disputes over mates, and bigger muscles give them an advantage.
But it is kick-boxing where kangaroos really excel. With his opponent in a solid headlock, a dominant male can drive the message home – balancing on his tail and pummelling with his powerful legs, which are tipped with sharp claws.
Kangaroos also kick in self-defence, as many unfortunate Australian dog-walkers can attest. And speaking of kicks, a kick from a hoof can leave an even greater impression.
Anyone that has spent time with horses know they can deliver a mean kick, especially if they buck to deliver a blow with both hind feet.
A zebra's kick is rumoured to be even more menacing, but the evidence to support this is purely anecdotal. Zebras are known to be harder to tame than horses, which might be why the idea that their kicks are more savage is so widespread.
The secretarybird may look pretty ridiculous, but it feeds on venomous snakes
Tim Caro of the University of California Davis has dedicated much of his career to studying zebras – even going so far as to dress up as a zebra to study them in the wild. In his 2016 book Zebra Stripes, he describes how plains zebras deal with predators. Video footage has shown that the zebras kick lions in the chest, but there is no scientific record of these kicks being fatal.
Other beasts that can really stick the boot in include ostriches and giraffes. Both have been recorded kicking out at, and wounding, large predators. In 2016, Planet Earth II gave us remarkable footage of a giraffe besting a lion with a well-placed kick. When you consider the ferocious jaws that might be snapping at their heels, it is little wonder that these animals can punt some serious punishment.
Yet these defensive moves are not intended to kill so much as repel. While a chance blow to a spine or jaw could prove deadly, the kicks are mostly a distraction to give the leggy prey animals a chance to run for safety.
For truly lethal strikes, we need to look at predators – especially those with difficult diets.
Stalking through the grasslands of sub-Saharan Africa is a predator researchers have described as a "ninja eagle on stilts". The secretarybird may look pretty ridiculous, but it feeds on venomous snakes, dispatching them with a single violent kick to the head.
Zebras are known to be harder to tame than horses
In a 2016 study, scientists measured the kicking ability of a captive male secretarybird called, for reasons that are not immediately clear, Madeleine. They found that Madeleine could deliver five or six times his own bodyweight in a tenth of the time it takes a human to blink.
This same hunting style may also have been employed by some of the aptly-named terror birds: huge flightless birds that lived in prehistoric South America. Members of the Mesembriornis genus had very strong legs, according to analyses of recovered bone fragments. This has prompted scientists to suggest that the birds might have dished out bone-shattering kicks, as a way to access the nutritious bone marrow of their prey.
Perhaps we should all forget about floating like a butterfly and stinging like a bee, and instead focus on punching like a shrimp and kicking like a bird.