But if it isn't the wind, what can it be ?" Phil Evans got out the best blade of his knife and set to work on the wall near the door.

Perhaps he might make a hole which would enable him to open it from the outside should it be only bolted or should the key have been left in the lock.

He worked away for some minutes.
The only result was to nip up his knife, to snip off its point, and transform what was left of the blade into a saw.
"Doesn't it cut ?" asked Uncle Prudent.
"No." "Is the wall made of sheet iron ?" "No; it gives no metallic sound when you hit it." "Is it of ironwood ?" "No; it isn't iron and it isn't wood." "What is it then ?" "Impossible to say.

But, anyhow, steel doesn't touch it." Uncle Prudent, in a sudden outburst of fury, began to rave and stamp on the sonorous planks, while his hands sought to strangle an imaginary Robur.
"Be calm, Prudent, be calm! You have a try." Uncle Prudent had a try, but the bowie-knife could do nothing against a wall which its best blades could not even scratch.

The wall seemed to be made of crystal.
So it became evident that all flight was impracticable except through the door, and for a time they must resign themselves to their fate--not a very pleasant thing for the Yankee temperament, and very much to the disgust of these eminently practical men.