I just call because you should be able to get all his chips if he has an overpair anyways, but he might just be bluffing with A-K. It's true that a "scare card" might fall on the turn, but when the pot is huge like this, most players disregard certain scare cards and just keep betting huge in an attempt to take down the pot. Also, there's a chance he might fold an overpair when I make a play that obviously indicates I can beat one.