Don't Let The Computer Bugs Byte

The computer knows where the migrating bug is at all times. 
It knows where it is because it knows where it was. 
By subtracting where it was from where it is, 
the computer is able to determine where it will be. 
Of course, 
if it isn't where it is, 
the error is due to where it wasn't 
and will propagate itself to where it won't be. 
Thus, the need for a Bug Filter - 
to decipher where it was from where it wasn't, 
thus allowing us to discriminate where the bug will be 
from where it won't be.

(This poem was inspired by a clever written description of a GPS satellite. Submitted into a contest with the word "bug" as a prompt.)