Sound of Thunder by Ray Bradbury

Time Safari advertises in the following way;

TIME SAFARI, INC.

SAFARIS TO ANY YEAR IN THE PAST.

YOU NAME THE ANIMAL.

WE TAKE YOU THERE.

YOU SHOOT IT.

The company official also says;

"We guarantee nothing," said the official, "except the dinosaurs."

Look like Safari Inc is a high end hunting expedition, extremely expensive ($10,000), and quite dangerous. Time travel for hunters!

How does Travis explain the chain of cause and effect that he says would occur if a hunter accidentally killed even one mouse?