Cobwebs from an Empty Skull

People who wear tight hats will do well to lay this fable well to heart, and ponder upon the deep significance of its moral: 

In passing over a river, upon a high bridge, a cow discovered a broad loose plank in the flooring, sustained in place by a beam beneath the centre.

“Now,” said she, “I will stand at this end of the trap, and when yonder sheep steps upon the opposite extreme there will be an upward tendency in wool.”

So when the meditative mutton advanced unwarily upon the treacherous device, the cow sprang bodily upon the other end, and there was a fall in beef.