grenade explosion w/ intact pin?

Ok, I was wondering if anyone else caught this, other than me. I was watching VvV earlier, and it struck me as odd. In Chapter 2, about 8 minutes into the movie, Gung Ho throws a grenade down the side of the pyramid, and beans a B.A.T. (I totally cracked up at that part.) The B.A.T.'s surrounding it all stop and form a circle around the grenade and stare at it. (8.03 on the timer) We can obviously see that the pin is still intact. Yet four seconds later, that same grenade explodes, sending the B.A.T.s flying. Now, any idiot knows that, with the pin still intact, the grenade isn't primed. I mean, it's just common sense.