This is a very intresting trick that could be used to annoy players in malls and such... Requires good timing through.
All you really have to do is cast a channeled aoe spell like a warlocks rain of fire or a mages Blizzard, as SOON as you see the cast bar pop up jump or move asap! It should show the animation there, and you can do it multiple time in differnt locations...
The only thing that sucks is that this effect disapeers when you get far away enough or relog.