Evidently the last man through had tried to cover up the hole, but had found the stone too heavy.

The Sikhs dragged it clear and disclosed the mouth of a tunnel, rather less than a man's height, sloping sharply downward.
"What we need now is mustard gas.

Smoke 'em out," said Goodenough.
"Might kill 'em," Grim objected.
"That'd be too bad, wouldn't it!" "We could starve 'em out, for that matter," said Grim.

"But they've probably got water down there, and perhaps food.

Every hour of delay adds to the risk of rioting.