Hundreds of thousands of wheels and ball bearings embedded into the floor of the facility, the lift and even the airplanes make pulling the hefty containers possible for between one and four mortal humans.

ENGADGET: Inside UPS' Worldport: How a shipping titan moves 2,000 packages every 17 seconds

The next night it's four vampires and six humans, then eight vampires and two humans.

NPR: So, What Actually Is 'Mathematically Impossible'?

The area's ecology previously had been deemed so fragile that humans were banned four months of the year.

FORBES: It's Not Easy Being Green

It seems that as long as humans embrace animals as four-legged friends, those bonds will continue past the pet's expiration date.

NPR: Mo. Taxidermist Preserves Man's Best Friend

Sikeliote craftsmen became the masters of the ancient world at carving microscopically detailed dies from which gold and silver coins were stamped in a great variety of intricate images not just of gods and humans, but of flying four-horse chariots and great eagles devouring their prey.

WSJ: Sicily's Proud Past | Sicily: Art and Invention Between Greece and Rome | J. Paul Getty Museum By David Littlejohn

Just like humans, airplane passengers of the four-legged variety must also contend with the risk of respiratory infections, dehydration and sleep deprivation.

CNN: Flying high: From 'cattle-class' to 'horse-class'

The animals here are accustomed to humans so boats can often approach to within four or five metres.

BBC: Brazil��s land of the jaguar

Chimpanzees were nearly four times more likely to wait for the big reward than humans were.

ECONOMIST: Evolution

Four such different (novel) virus subtypes have appeared in humans since the global epidemic (pandemic) of 1918, which killed tens of millions of people.

CNN: Influenza (flu)

The arrests are part of a wider French inquiry into the deaths of at least four people in France from variant CJD that is passed onto humans by eating beef.

BBC: French restaurant chain in BSE probe