[oneijoe]

There are rules about the huddle that prevent the snake in the grass play from being legal.

That's true. It's also why P-burg ran it out of a no-huddle offense.

The receiver was talking back and forth to the sideline, while he was -apparantly- moving off the field ("Don't make me come out, coach !"). But...he stays within the legal distance to the end of the offensive line (meaning this player was really nothing more than "in motion"), QB quicksnaps and hits the receiver on a go route.

There was NO substitute that came in between plays. The offense used the between plays confusion to make it appear that way, though.