Engulfing Darkness messages
 

The spell description shows that Cast on Other displays a : is engulfed by darkness. message.
I use GTT to check the length left on the snare, and I remarked that when the snare wears off the mob, then the Cast on Other message is displayed again instead of the Wears Off message which should be The darkness fades

What is GTT?

GamTextTriggers from http://www.gambosoft.com/