[Andy B]

I would fold fourth. I would check fifth and probably call one bet. It looks like the guy behind you has made a low, so you're playing for half of a very small pot and you have one pair. Folding can't be too far wrong. On the river, your call closes the action. The guy with open Sixes sure seems like he was on a low draw, so he could as easily be calling with a low as with two pair. I pay it off.