After many millions of years of evolution, the very first elephant appeared on Earth. He was a strange sort of creature, with a kind and gentle heart. But, as he was very big, many feared him. He was lonely.
Just around that same time, the very first mouse came about. He was bold and energetic. But he was too small to be significant. He was lonely.
One day it came to pass that the lonely elephant and the lonely mouse were the only creatures at the watering hole. The elephant (having frightened the other animals away) and the mouse (assuming that he would go unnoticed) drank in silence. But then, the elephant spotted the mouse, out of the corner of his great big eye.
"Why hello." He said tentatively.
The mouse glanced around to see who the elephant was addressing. Then, realizing it was himself, he raised himself onto his haunches to respond.
"Hello." He replied.
The two animals simply looked at each other for a while. Sizing each other up, they each noticed something foreign in the other's eyes: The elephant saw bravery. The mouse saw kindness.
Then they began to talk. Cautiously at first -- about the weather and evolution -- but then with abandon. About philosophy and about life and about what it was like to be so big, and so

small.

And at the same time each day afterward, the two not-so-lonely animals would meet to run and talk and play. Each enjoyed the other's company immensely, and they became the closest of friends. Life had never been better.
One morning several months later, the elephant awoke and set out to meet the mouse as usual. He reached the grassy knoll that was their meeting place and waited.
And waited.
The mouse remained absent. Although the elephant wasn't too good with time, he could tell he had been waiting for quite a while because the hot sun was already high in the sky.
And was it ever hot! The heat rose in rippling waves from the ground. Sweat trickled down the elephant's domed brow and into his eyes. He felt somewhat sick with the heat. But he worried only for his friend. Where could he be?
The elephant raised a front foot to shield his eyes from the sun when he saw the mouse. But not approaching happily on the horizon -- on the bottom of his own foot.
The elephant reeled in shock and horror, not believing what he had done. The mouse, his only friend. Dead. And by his error! He cradled the tiny body as tears and sweat and grief poured out of him. The only thing more unbearable than his guilt was the glassy look of the mouse's once-so-lively eyes.

Many years passed. The elephant fell into a horrible depression. Other elephants appeared on Earth, but he preferred to remain alone with the memory of his old friend. He did, however, manage to find himself an elephant wife who did not mind his grave disposition. He and his wife had themselves an elephant family.
Of all the things the elephant taught his children, there was one that he believed to be most important. To spare his offspring and their offspring from the guilt and grief he suffered every day of his life, he told them most sternly to avoid mice at all costs.
When they asked him why, he told them only:
"Because if you don't, then you shall surely die."