There are two steps to using a grenade: pulling the pin, and throwing the grenade as far away as humanly possible. Apparently the second part is a little difficult for some people.
A Chinese army recruit got the first part down, but he made a nearly tragic mistake when it came to actually throwing the grenade. When he wound his arm back to throw the grenade slipped out of his hand.
The instructor was on his game though, he pulled the recruit into a trench before the grenade exploded and threw shrapnel everywhere.