Sometimes when you can't solve a problem it's very easy to prove that it can't be solved by anyone.

That's what I can prove now, but why waste time ?" "Have we got anything special to do with our time ?" asked Ronicky dryly.
"Well, my proof is easy.

Here we are in hard-pan dirt, without any sort of a tool for digging.

So we sure can't tunnel out from the sides, can we ?" "Looks most like we can't," said Ronicky sadly.
"And the only ways that are left are the ends." "That's right." "But one end is the unfinished part of the tunnel; and, if you think we can do anything to the steel door--" "Hush up," said Ronicky.

"Besides, there ain't any use in you talking in a whisper, either.