Trigger Match Problem

I have a trigger match that constantly changes. how do I trigger it.
A prickly stinging overcomes your body, fading away into numbness.

It can change into:
A prickly*stinging o*ercomes your body, fading away into*numbness.
A pr*ckly*stining overcomes your*body, fading away into numbness.

All sorts of stuff like that. How would I got about triggering it?

Heh, this trigger comes up so often it deserves a forum section of its own by now :)

But check this thread for the answer:
http://www.gammon.com.au/forum/bbshowpost.php?bbsubject_id=2178