Sly humor

I'm still reading William Mayne's "Sand"(1964)...such wonderful writing you have to read it slowly. His humor and characterizations are so sly you have to pay careful attention. The writing made me laugh out loud, which doesn't happen much...

Some background: The boys in this story found a small railway hidden under the sand for hauling gravel at some now defunct gravel company. They want to unearth the tracks, but it passes through a neighbor's property. The neighbor does not want their property dug up. The boys figure a way around this...

"'Dear sir,'" read Bobby. "'I regret I cannot allow you
to expose the rails under the road to my house. Yours faith-
fully, N.Merriot.'"
"I wonder what he means, exactly," said Harold, look-
ing slyly at Ainsley, to see whether he appreciated the joke.
"We could say we thought it meant something else,"
said Ainsley. "But it would be a waste of a good lie."
"We should have let Guy read it," said Bobby. "He
could make it mean anything."
They went out to see what Guy could make it into. Guy
read it, and without any prompting he decided that to
regret you cannot allow something means that you are sorry
that the thing is not being done, and therefore if anyone
wanted to do it, they would be welcome.
"You must be right," said Harold. "We ought to have
made you do it in the beginning."
"We caught ourselves," said Bobby. "Who would dare
to explain that we mean what Guy means." (page 127, "Sand")

A deceptively funny story...and yet another reason I continue to read William Mayne.