When Professor Henry Hassel discovers his wife in the arms of another man, he does what any
mad scientist would do: build a time machine to go back and kill his wife’s grandfather. He
has no trouble changing the past, but any effect on the present seems rather harder to
achieve.
“While I was backing up, I inadvertently trampled and killed a small Pleistocene
insect.”
“Aha!” said Hassel.
“I was terrified by the indicent. I had visions
of returning to my world to find it completely changed as a result of this single death.
Imagine my surprise when I returned to my world to find that nothing had changed!”