Eckels is ready to embark on his journey to the past, and has his 10,000 dollar check ready to be passed in and made official.
As Eckels travels through time with is safari leaders, Mr. Travis and Lesperance, be begins to feel a bit uneasy, and starts to regret his decision.
One of the biggest rules of this safari is to not leave The Path, so nothing from the past gets affected, and so the future doesn't completely change.
The adventurers encounter the T rex, but Eckels loses his senses, as a result of fear, and steps off The Path, while the others kill the dinosaur.
As they travelled home, Travis is very worried and angry that Eckels may have messed something up in the future by stepping off The Path.
Eckels realizes that by stepping off The Path, he had changed spellings of words, and more importantly, changed the outcome of the presidential election, just by killing a singular butterfly. There was a sound of thunder.