Cow Magnets Are Large (Strong) Magnets Cows Are Made To Swallow That   
Attract The Bits Of Metal That A Cow Might Be Unfortunate Enough To Eat.

I Imagine That On The Fuel Line, It Would Serve Largely The Same Purpose.
(Which, By THe Way Sounds Like A Good Idea!)
 -Eric B.

******cow magnets on the fuel line?  what is that rumored to do?*****