Let's say the SPY is sitting at 87. The SPY 87 calls are 6.70 bid, offered at 7.30. Somebody comes in wanting to buy 10,000 of those calls. He buys all the calls offered at 7.30, then buys all the calls offered at 7.35, then all the calls offered at 7.40, etc.
By the time he's done, he's...