Confidently they ducked their big, round heads and dived down the old entrance, only to be brought up with a bump when they had gone about three feet.

Out they came in a rage, fluffing their feathers and snapping their beaks, and stood on each side of the hole to talk the affair over.

First, one and then the other reentered to investigate.

They found it quite inexplicable.
They felt sure this _was_ the way they had previously entered--so sure, in fact, that again and again they tried it, only growing more and more puzzled and indignant with each attempt.

Finally they came to the conclusion that they must have made some mistake.