I'm not an expert by any means, so someone correct me if I'm wrong. I've in the OEX pit myself, and actually met the guy that faciliates my orders from my broker (think or swim). When an order came in that was marketable, he would yell out, and thus the price discovery began.
If you watch CBOETV, they film the afternoon segments in the OEX pit every day, so you can kind of see whats going on sometimes in the pit.