Explosions are a great subject for effects animation.
Well, they are very dynamic and by nature, very non-uniform. The residuals of an explosion are another thing that makes them interesting as this often include flying debris, smoke, shockwaves, and even secondary explosions. There are so many different kinds of explosions too. The often unrealistic and overused effect in Hollywood is the fiery explosion, but this is usually the result of a volatile source like barrels of gasoline. However watching grenades go off is a totally different effect.