Playing with, "a Rock" - Straddle?

[StrayBullet]

I've done a search, so sorry if it's been hased, shuffle off to Beginner's if need be [img]/images/graemlins/grin.gif[/img]

I understand what a "rock" is but I'm unclear as to how it "creates action."

When does the rock ever get converted or come off the table, if nobody ever really "wins" the extra chips, then what's the incentive?