Mark Twain's Use of "[word removed in order to comply with Google's Publisher Policy] in the woodpile"

My stepson is reading Tom Sawyer and he ran across the phrase "[word removed in order to comply with Google's Publisher Policy] hiding in the woodpile." Does anyone know what this phrase means in a figurative sense?
Thanks,
Gabriela

A problem hidden from view. A potential unforseen obstacle. 19th century.