Why does everyone leave the eldorado and stand outside in sixty below zero weather?

Thornton had bet another man that Buck could pull a thousand pound sled.

Matthewson's sled, loaded with a thousand pounds of flour, had been standing for a couple of hours, and in the intense cold (it was sixty below zero) the runners had frozen fast to the hard-packed snow. Men offered odds of two to one that Buck could not budge the sled. A quibble arose concerning the phrase "break out."

All the men in the saloon run out to witness Buck's attempt. Thornton wins $1600.