Priest talent Spectral Guise.
Effectively a vanish but breakable. Most of the priests use shield before Guise-ing, prolonging the stealth effect on them, as 3 direct attacks /or bleeds in this case/ will cancel their buff.
You can instantly dispel Guise IF:
-priest did not put up shield
-used Guise in 8 yards of you
You Cat-Swipe and voila, priest is knocked out of stealth, instead of hitting his fake form with 3 direct attacks.
But, do not forget, shield will mess this up. Still keep an eye out for opportunities.