The REALLY BIG pointer to Gri'd 'speciality' in the movie is quite simply the massive masiveness of his tail. I mean look at the scene where he impales Chopper. That thing is MASSIVE.

He was smarter than the rest. That's most resonably the reason he was the alpha and why he got the drop on chopper and why he made it out alive aginst celtic. When Scar shot that plasma blast, he moved, unlike his brothers haha. simple as that