NOTE:   I don't know how anyone could write this with a straight face! 
This was an actual memo sent at an unnamed computer company to its 
employees.  It went to all the company's field engineers, and it was in 
regard to a computer peripheral problem. The author of this memo was
quite serious; the engineers rolled on the floor!  (Especially note the 
last sentence!) 

INSTRUCTIONS FOR REPLACING MOUSE BALLS 

Mouse balls are now available as FRU (Field Replacement Unit). 
Therefore, if a mouse fails to operate or should it perform erratically, 
it may need a ball replacement. Because of the delicate nature of this
procedure, replacement of mouse balls should only be attempted by  
properly trained personnel. 

Before proceeding, determine the type of mouse balls by examining the 
underside of the mouse. Domestic balls will be larger and harder than 
foreign balls. 

Ball removal procedures differ depending upon the manufacturer of the 
mouse. Foreign balls can be replaced using the pop-off method.  Domestic 
balls are replaced by using the twist-off method. 

Mouse balls are not usually static-sensitive.  However, excessive handling 
can result in sudden discharge. 

Upon completion of ball replacement, the mouse may be used immediately. 
It is recommended each replacer have a pair of spare balls for maintaining 
optimum customer satisfaction.  Any customer missing his balls should 
contact the local personnel in charge of removing and replacing these 
necessary items.