The butterfly effect

"A Sound of Thunder" is a 1952 science fiction short story by Ray Bradbury about a man who wants adventure, so he pays Time Safari to take him back in time to hunt a Tyrannosaurus Rex.  There are rules — like stay on the path, don’t touch the dirt, and only kill the dinosaur right before its natural death — so they don't do anything to radically alter the future. But the appearance of T-Rex is so terrifying that Eckels loses his nerve and runs away — and off the path.

Is it a spoiler if I tell you part of what happened?  (I won't explain "a sound of thunder.")

"Eckels felt himself fall into a chair. He fumbled crazily at the thick slime on his boots. He held up a clod of dirt, trembling ... Embedded in the mud, glistening green and gold and black, was a butterfly, very beautiful and very dead."

I read the story online, free.  It's illustrated with cartoon characters, like this.  But I like my butterfly illustration better.