It can be anything
For me:
First day of actually playing 40k, someone lets me use a chaos army in the middle of a game vs this really proud and cocky SM player
After a breef description of who and how could shoot/attack i choose my weapons, my target, roll some dice and a few bouncy rolls and boring counts later i find out i actually hit something
to my surprise i managed to break the morale of the most expensive SM squad on the table that happened to be really close to the sides...
The other guy goes all fuzzy, measures 4 times, moves his men... and then starts packing them
I was seriously left in the blue at that point
That`s when i found out the link between little plastic man and herd animals, they both jump of off cliffs in large numbers with no real reason
I know it doesn`t sound like much, but the look on the guys face after loosing a whole squad to someone who didn`t even knew why some dices have strange markings on them instead of numbers was pretty damn funny
That and the fact that all his buddies wouldn`t give him a break for the rest of the day :P