He could not understand it in the least.

He struck another.

It flashed, but like the others went out.
Then he suddenly remembered that Skipper Ed had once said fire would not burn in air from which the oxygen had been taken, for then the air would be "dead," and that a person would exhaust all the air in a close room in a short time, and therefore rooms should be well ventilated.

And with this he realized what had happened.

His air had been cut off and all that remained was dead.
The drift had covered his den to a great depth while he slept, and the wind had packed the snow so hard that the air could no longer circulate through it.
It was necessary that an opening be made quickly or he would smother, and this he set about to do with all his might.