A botanist was trying to research some details about a particular kind of fern, so he sent a request to all his colleagues, asking them to send him any information they had about it.

Unfortunately, he didn't word his request very well, and all the botanists he'd contacted thought he was looking for details about any ferns, rather than just the one species. So within just a few hours of sending it out, his fax machine was buzzing with piles of useless documents about all kinds of ferns - there were tree ferns and wood ferns, ostrich ferns and cinnamon ferns... but very few about the particular type he wanted.

So he sent another message to everyone:

If it ain't bracken, don't fax it.