Flies avoid being swatted in just the same way that Keanu Reeves dodges flying bullets in the movie The Matrix - by watching time pass slowly.

To the insect, that rolled up newspaper moving at lightning speed might as well be inching through thick treacle.

Like Reeves standing back and side-stepping slo-mo bullets, the fly has ample time to escape.

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And it is not alone in its ability to perceive time differently from us.

New research by Scots and Irish scientists suggests that across a wide range of species, time perception is directly related to size.

Generally the smaller an animal is, and the faster its metabolic rate, the slower time passes.

The evidence comes 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.

Professor Graeme Ruxton, from the University of St Andrews, took part in the research.

He 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."