War of the Felines!

Hi I have two cats one is about 6 or 7 years old and the other is only nine months, for some strange reason the older cat hisses and the younger. All my young cat, Smudge has to do is walk by the older cat (Gracie Mae) and the hissing begins. WHen Smudge was little Gracie use to mother her now its a matter of time before one or the other gets hurt.:confused:

What is going on? There are at least 5 threads in Cat Behavior devoted to "kitties gone wild". LOL Must be something in the stars. ;)