Quote from rmorse:
It's were the value is. Let's take a simple example. 10 days to expiration, stock trading at 40, I'm trading the 43 puts/calls, and the next day there will be a .25 dividend. Let's say the call is trading .05/.07. My market on the put would be 3.25/3.35. I'm willing to buy the put .25 over parity with the stock and get the call for free (-interest/comm). The following day, the stock I buy against the position will not receive the dividend. All things equal, my call market might drop to .04/.06, but only from decay. My put market would now be 3.00/3.10, again looking to get the call for free with the hedge.