Flies avoid being swatted in the same way Keanu Reeves dodges flying bullets in The Matrix, by watching time pass slowly, research suggests.
The smaller an animal is, and the faster its metabolic rate, the slower time passes for it, scientists found.
This means that across a wide range of species, time perception is directly related to size, with animals smaller than us seeing the world in slow motion.
The findings, published in the journal Animal Behaviour, come from research into the ability of animals to detect separate flashes of fast-flickering light.
"Critical flicker fusion frequency" - the point at which the flashes seem to merge together, so that a light source appears constant - provides an indication of time perception.
Comparing studies of the phenomenon in different animals revealed the link with size.
Dr Andrew Jackson, from Trinity College Dublin, who led the study, said: "A lot of researchers have looked at this in different animals by measuring their perception of flickering light.
"Some can perceive quite a fast flicker and others much slower, so that a flickering light looks like a blur.
"Interestingly, there's a large difference between big and small species. Animals smaller than us see the world in slo-mo. It seems to be almost a fact of life.
“Our focus was on vertebrates, but if you look at flies, they can perceive light flickering up to four times faster than we can.
"You can imagine a fly literally seeing everything in slow motion."
The effect may also account for the way time seems to speed up as we get older, Dr Jackson said.
He decided to conduct the study after noticing the way small children always seem to be in such a hurry.
"It's tempting to think that for children time moves more slowly than it does for grown ups, and there is some evidence that it might," he said.
"People have shown in humans that flicker fusion frequency is related to a person's subjective perception of time, and it changes with age. It's certainly faster in children."
More than 30 species were studied for the research, including rodents, eels, lizards, chickens, pigeons, dogs, cats and leatherback turtles.
Kevin Healy, a Phd student at the School of Natural Sciences at Trinity College Dublin and co-author of the study, said: "Our results lend support to the importance of time perception in animals where the ability to perceive time on very small scales may be the difference between life and death for fast-moving organisms."
Professor Graeme Ruxton, from the University of St Andrews in Scotland, who also took part in the research, said: "Having eyes that send updates to the brain at much higher frequencies than our eyes do is of no value if the brain cannot process that information equally quickly.
“Hence, this work highlights the impressive capabilities of even the smallest animal brains.
"Flies might not be deep thinkers, but they can make good decisions very quickly."
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