Рэй Брэдбери - A Sound of Thunder

It fell to the floor, an exquisite thing, a small thing that could upset balances and knock down a line of small dominoes and then big dominoes and then gigantic dominoes, all down the years across Time. Eckels' mind whirled. It couldn't change things. Killing one butterfly couldn't be that important! Could it?

His face was cold. His mouth trembled, asking: «Who — who won the presidential election yesterday?»

The man behind the desk laughed. «You joking? You know very well. Deutscher, of course! Who else? Not that fool weakling Keith. We got an iron man now, a man with guts!» The official stopped. «What's wrong?»

Eckels moaned. He dropped to his knees. He scrabbled at the golden butterfly with shaking fingers. «Can't we,» he pleaded to the world, to himself, to the officials, to the Machine, «can't we take it back, can't we make it alive again? Can't we start over? Can't we―»

He did not move. Eyes shut, he waited, shivering. He heard Travis breathe loud in the room; he heard Travis shift his rifle, click the safety catch, and raise the weapon.

There was a sound of thunder.