Maybe An Old One

You can take your dog running, but you have to be careful about taking him too far. Why is that?

Most mammals can sprint faster than humans — having four legs gives them the advantage. But when it comes to long distances, humans can outrun almost any animal. Because we cool by sweating rather than panting, we can stay cool at speeds and distances that would overheat other animals. On a hot day, the two scientists wrote, a human could even outrun a horse in a 26.2-mile marathon.

No matter how long you make the course,
I'm doubtful I could beat a horse.

But I'm willing to run the experiment
for the sake of general merriment