A CATS TAIL GOES BACK,AND FORTH,BEFORE THEY PLAY,I THINK,THATS ITS JUST THIER WAY,OF GETTING THEMSELVES PSCHYED UP,A BIT,BEFORE THEY POUNCE,OR MAYBE,ITS TO HELP,WITH THE POUNCE,WITH THE TAIL,ACTING AS BALANCE.
AND WE HOPE,THATS ONLY A COLD,WE ARE PRAYING,FOR YOUR CAT!!