It's obviously a matter of judgment regarding what one deems to be "an attempt to advance." I think I have always applied the rule moreso in accordance with J/R's statement regarding the rule:
A batter-runner over-running first base who subsequently takes a single step (or steps) toward second base with intent to advance [my emphasis] is no longer over-running and can be tagged out while off base.
I find it difficult to think that without a single step that a runner could be attempting advance. BR obviously is not going to make a "dive" into 2nd base from his location after overrunning 1B. Of course, this doesn't mean that a single step toward 2B constitutes a runner attempting to advance to 2nd. He may have just turned toward 2B after overrunning 1B, which is legal.
Combine that "flinch" with a single step, then I've got an attempt to advance, but the flinch only without any step in that direction I would not judge to be an "attempt to advance." I think a flinch only without any step may be considered booger picking. IMO, I hope your flinch included at least a single step when you declared the runner out. A quick turn to see what occurred on the play might be judged as a flinch, but no decision on advancing may have been made by the runner. The step with the flinch proves that decision was made---if only briefly.
I think this is a situation where J/R provides just a little extra information than JEA in their attempt to provide guidance on making this calll.
Just my opinion,
Freix
[Edited by Bfair on Jan 10th, 2002 at 08:57 AM]